Configuration sharing from SDK client to credentials provider

Created a LambdaClient as follows:

`

httpClientBuilder =
ApacheHttpClient.builder()
.proxyConfiguration(
proxyConfig
.endpoint(URI.create("http://myproxy.com:8080"))
.username("username")
.password("password")
.build());

client =
LambdaClient.builder()
.httpClientBuilder(httpClientBuilder)
.region(region)
.build();
`

In SdkDefaultClientBuilder being called internally from DefaultStsClientBuilder, I see that the httpClient is being created with an empty proxyConfiguration.

## Expected Behavior
Sts should use the same proxyConfigration as the one I passed to the LambdaClient.

## Current Behavior
Proxy is not used, and thus the host is not resolvable.

`
software.amazon.awssdk.core.exception.SdkClientException: Unable to execute HTTP request: sts.amazonaws.com
at software.amazon.awssdk.core.exception.SdkClientException$BuilderImpl.build(SdkClientException.java:97)
at software.amazon.awssdk.core.internal.http.pipeline.stages.RetryableStage$RetryExecutor.handleThrownException(RetryableStage.java:164)
at software.amazon.awssdk.core.internal.http.pipeline.stages.RetryableStage$RetryExecutor.execute(RetryableStage.java:117)
at software.amazon.awssdk.core.internal.http.pipeline.stages.RetryableStage.execute(RetryableStage.java:67)
at software.amazon.awssdk.core.internal.http.pipeline.stages.RetryableStage.execute(RetryableStage.java:47)
at software.amazon.awssdk.core.internal.http.pipeline.RequestPipelineBuilder$ComposingRequestPipelineStage.execute(RequestPipelineBuilder.java:205)
at software.amazon.awssdk.core.internal.http.StreamManagingStage.execute(StreamManagingStage.java:56)
at software.amazon.awssdk.core.internal.http.StreamManagingStage.execute(StreamManagingStage.java:41)
at software.amazon.awssdk.core.internal.http.pipeline.RequestPipelineBuilder$ComposingRequestPipelineStage.execute(RequestPipelineBuilder.java:205)
at software.amazon.awssdk.core.internal.http.pipeline.RequestPipelineBuilder$ComposingRequestPipelineStage.execute(RequestPipelineBuilder.java:205)
at software.amazon.awssdk.core.internal.http.pipeline.stages.ExecutionFailureExceptionReportingStage.execute(ExecutionFailureExceptionReportingStage.java:37)
at software.amazon.awssdk.core.internal.http.pipeline.stages.ExecutionFailureExceptionReportingStage.execute(ExecutionFailureExceptionReportingStage.java:25)
at software.amazon.awssdk.core.internal.http.AmazonSyncHttpClient$RequestExecutionBuilderImpl.execute(AmazonSyncHttpClient.java:272)
at software.amazon.awssdk.core.client.handler.BaseSyncClientHandler.invoke(BaseSyncClientHandler.java:90)
at software.amazon.awssdk.core.client.handler.BaseSyncClientHandler.execute(BaseSyncClientHandler.java:102)
at software.amazon.awssdk.core.client.handler.BaseSyncClientHandler.execute(BaseSyncClientHandler.java:67)
at software.amazon.awssdk.core.client.handler.SdkSyncClientHandler.execute(SdkSyncClientHandler.java:44)
at software.amazon.awssdk.awscore.client.handler.AwsSyncClientHandler.execute(AwsSyncClientHandler.java:53)
at software.amazon.awssdk.services.sts.DefaultStsClient.assumeRole(DefaultStsClient.java:239)
at software.amazon.awssdk.services.sts.auth.StsAssumeRoleCredentialsProvider.getUpdatedCredentials(StsAssumeRoleCredentialsProvider.java:68)
at software.amazon.awssdk.services.sts.auth.StsCredentialsProvider.updateSessionCredentials(StsCredentialsProvider.java:68)
at software.amazon.awssdk.utils.cache.CachedSupplier.refreshCache(CachedSupplier.java:133)
at software.amazon.awssdk.utils.cache.CachedSupplier.get(CachedSupplier.java:90)
at software.amazon.awssdk.services.sts.auth.StsCredentialsProvider.resolveCredentials(StsCredentialsProvider.java:78)
at software.amazon.awssdk.services.sts.auth.StsAssumeRoleCredentialsProvider.resolveCredentials(StsAssumeRoleCredentialsProvider.java:42)
at software.amazon.awssdk.services.sts.internal.StsProfileCredentialsProviderFactory$StsProfileCredentialsProvider.resolveCredentials(StsProfileCredentialsProviderFactory.java:93)
at software.amazon.awssdk.awscore.internal.client.handler.AwsClientHandlerUtils.createExecutionContext(AwsClientHandlerUtils.java:54)
at software.amazon.awssdk.awscore.client.handler.AwsSyncClientHandler.createExecutionContext(AwsSyncClientHandler.java:65)
at software.amazon.awssdk.core.client.handler.BaseSyncClientHandler.execute(BaseSyncClientHandler.java:62)
at software.amazon.awssdk.core.client.handler.SdkSyncClientHandler.execute(SdkSyncClientHandler.java:44)
at software.amazon.awssdk.awscore.client.handler.AwsSyncClientHandler.execute(AwsSyncClientHandler.java:53)
at software.amazon.awssdk.services.sts.DefaultStsClient.assumeRole(DefaultStsClient.java:239)
at software.amazon.awssdk.services.sts.auth.StsAssumeRoleCredentialsProvider.getUpdatedCredentials(StsAssumeRoleCredentialsProvider.java:68)
at software.amazon.awssdk.services.sts.auth.StsCredentialsProvider.updateSessionCredentials(StsCredentialsProvider.java:68)
at software.amazon.awssdk.utils.cache.CachedSupplier.refreshCache(CachedSupplier.java:133)
at software.amazon.awssdk.utils.cache.CachedSupplier.get(CachedSupplier.java:90)
at software.amazon.awssdk.services.sts.auth.StsCredentialsProvider.resolveCredentials(StsCredentialsProvider.java:78)
at software.amazon.awssdk.services.sts.auth.StsAssumeRoleCredentialsProvider.resolveCredentials(StsAssumeRoleCredentialsProvider.java:42)
at software.amazon.awssdk.services.sts.internal.StsProfileCredentialsProviderFactory$StsProfileCredentialsProvider.resolveCredentials(StsProfileCredentialsProviderFactory.java:93)
at software.amazon.awssdk.auth.credentials.ProfileCredentialsProvider.resolveCredentials(ProfileCredentialsProvider.java:110)
at software.amazon.awssdk.awscore.internal.client.handler.AwsClientHandlerUtils.createExecutionContext(AwsClientHandlerUtils.java:54)
at software.amazon.awssdk.awscore.client.handler.AwsSyncClientHandler.createExecutionContext(AwsSyncClientHandler.java:65)
at software.amazon.awssdk.core.client.handler.BaseSyncClientHandler.execute(BaseSyncClientHandler.java:62)
at software.amazon.awssdk.core.client.handler.SdkSyncClientHandler.execute(SdkSyncClientHandler.java:44)
at software.amazon.awssdk.awscore.client.handler.AwsSyncClientHandler.execute(AwsSyncClientHandler.java:53)
at software.amazon.awssdk.services.lambda.DefaultLambdaClient.invoke(DefaultLambdaClient.java:1078)
at com.mytest.ITLambda.tes(ITLambda.java:58)
Caused by: java.net.UnknownHostException: sts.amazonaws.com
at java.net.InetAddress.getAllByName0(InetAddress.java:1280)
at java.net.InetAddress.getAllByName(InetAddress.java:1192)
at java.net.InetAddress.getAllByName(InetAddress.java:1126)
at org.apache.http.impl.conn.SystemDefaultDnsResolver.resolve(SystemDefaultDnsResolver.java:45)
at org.apache.http.impl.conn.DefaultHttpClientConnectionOperator.connect(DefaultHttpClientConnectionOperator.java:112)
at org.apache.http.impl.conn.PoolingHttpClientConnectionManager.connect(PoolingHttpClientConnectionManager.java:373)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at software.amazon.awssdk.http.apache.internal.conn.ClientConnectionManagerFactory$Handler.invoke(ClientConnectionManagerFactory.java:80)
at com.sun.proxy.$Proxy0.connect(Unknown Source)
at org.apache.http.impl.execchain.MainClientExec.establishRoute(MainClientExec.java:381)
at org.apache.http.impl.execchain.MainClientExec.execute(MainClientExec.java:237)
at org.apache.http.impl.execchain.ProtocolExec.execute(ProtocolExec.java:185)
at org.apache.http.impl.client.InternalHttpClient.doExecute(InternalHttpClient.java:185)
at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:83)
at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:56)
at software.amazon.awssdk.http.apache.internal.impl.ApacheSdkHttpClient.execute(ApacheSdkHttpClient.java:72)
at software.amazon.awssdk.http.apache.ApacheHttpClient.execute(ApacheHttpClient.java:200)
at software.amazon.awssdk.http.apache.ApacheHttpClient.access$400(ApacheHttpClient.java:92)
at software.amazon.awssdk.http.apache.ApacheHttpClient$1.call(ApacheHttpClient.java:178)
at software.amazon.awssdk.http.apache.ApacheHttpClient$1.call(ApacheHttpClient.java:175)
at software.amazon.awssdk.core.internal.http.pipeline.stages.MakeHttpRequestStage.executeHttpRequest(MakeHttpRequestStage.java:58)
at software.amazon.awssdk.core.internal.http.pipeline.stages.MakeHttpRequestStage.execute(MakeHttpRequestStage.java:50)
at software.amazon.awssdk.core.internal.http.pipeline.stages.MakeHttpRequestStage.execute(MakeHttpRequestStage.java:34)
at software.amazon.awssdk.core.internal.http.pipeline.RequestPipelineBuilder$ComposingRequestPipelineStage.execute(RequestPipelineBuilder.java:205)
at software.amazon.awssdk.core.internal.http.pipeline.RequestPipelineBuilder$ComposingRequestPipelineStage.execute(RequestPipelineBuilder.java:205)
at software.amazon.awssdk.core.internal.http.pipeline.RequestPipelineBuilder$ComposingRequestPipelineStage.execute(RequestPipelineBuilder.java:205)
at software.amazon.awssdk.core.internal.http.pipeline.RequestPipelineBuilder$ComposingRequestPipelineStage.execute(RequestPipelineBuilder.java:205)
at software.amazon.awssdk.core.internal.http.pipeline.RequestPipelineBuilder$ComposingRequestPipelineStage.execute(RequestPipelineBuilder.java:205)
at software.amazon.awssdk.core.internal.http.pipeline.stages.RetryableStage$RetryExecutor.doExecute(RetryableStage.java:139)
at software.amazon.awssdk.core.internal.http.pipeline.stages.RetryableStage$RetryExecutor.execute(RetryableStage.java:109)
... 57 more
`

## Possible Solution
Pass proxy configuration to Sts client.

* AWS Java SDK version used: 2.0.0-preview-12
* JDK version used:1.8.0_171
* Operating System and version: MacOS 10.13.6

Start with the LambdaClient builder flow and inspect SdkDefaultClientBuilder when it creates a DefaultStsClientBuilder for the credentials provider. Reproduce the proxyConfiguration setup against the reported UnknownHostException, then verify that the STS client uses the same proxy configuration and that the Lambda request succeeds.

Written by the indexing model from the issue text.