Host startup error when retrieving latest Extension Bundles version info throws

When we try to retrieve the bundle version index, we check if the request was successful. In case it wasn't, we log an error and return null, to let the caller decide.

https://github.com/Azure/azure-functions-host/blob/0058f8befdb9bb9da5cb9ac183896590a02f2cbf/src/WebJobs.Script/ExtensionBundle/ExtensionBundleManager.cs#L225-L236

However, the request can fail in a less graceful way, for example throwing an exception, breaking the flow and the startup operation. One example could be a VNET integrated app with a firewall that abruptly ends the connection:

```csharp
System.Net.Http.HttpRequestException : The SSL connection could not be established, see inner exception. --->
System.IO.IOException : Authentication failed because the remote party has closed the transport stream.
at System.Net.Security.SslStream.StartReadFrame(Byte[] buffer,Int32 readBytes,AsyncProtocolRequest asyncRequest)
at System.Net.Security.SslStream.PartialFrameCallback(AsyncProtocolRequest asyncRequest)
at System.Net.Security.SslStream.ThrowIfExceptional()
at System.Net.Security.SslStream.InternalEndProcessAuthentication(LazyAsyncResult lazyResult)
at System.Net.Security.SslStream.EndProcessAuthentication(IAsyncResult result)
at System.Net.Security.SslStream.EndAuthenticateAsClient(IAsyncResult asyncResult)
at System.Net.Security.SslStream.<>c.b__65_1(IAsyncResult iar)
at System.Threading.Tasks.TaskFactory`1.FromAsyncCoreLogic(IAsyncResult iar,Func`2 endFunction,Action`1 endAction,Task`1 promise,Boolean requiresSynchronization)
at async System.Net.Http.ConnectHelper.EstablishSslConnectionAsyncCore(Stream stream,SslClientAuthenticationOptions sslOptions,CancellationToken cancellationToken)
at async System.Net.Http.HttpConnectionPool.ConnectAsync(HttpRequestMessage request,Boolean allowHttp2,CancellationToken cancellationToken)
at async System.Net.Http.HttpConnectionPool.CreateHttp11ConnectionAsync(HttpRequestMessage request,CancellationToken cancellationToken)
at async System.Net.Http.HttpConnectionPool.GetHttpConnectionAsync(HttpRequestMessage request,CancellationToken cancellationToken)
at async System.Net.Http.HttpConnectionPool.SendWithRetryAsync(HttpRequestMessage request,Boolean doRequestAuth,CancellationToken cancellationToken)
at async System.Net.Http.RedirectHandler.SendAsync(HttpRequestMessage request,CancellationToken cancellationToken)
at async System.Net.Http.HttpClient.FinishSendAsyncBuffered(Task`1 sendTask,HttpRequestMessage request,CancellationTokenSource cts,Boolean disposeCts)
at async Microsoft.Azure.WebJobs.Script.ExtensionBundle.ExtensionBundleManager.GetLatestMatchingBundleVersionAsync(??) at /src/azure-functions-host/src/WebJobs.Script/ExtensionBundle/ExtensionBundleManager.cs : 234
at async Microsoft.Azure.WebJobs.Script.ExtensionBundle.ExtensionBundleManager.GetBundle(HttpClient httpClient) at /src/azure-functions-host/src/WebJobs.Script/ExtensionBundle/ExtensionBundleManager.cs : 107
at async Microsoft.Azure.WebJobs.Script.ExtensionBundle.ExtensionBundleManager.GetExtensionBundlePath(??) at /src/azure-functions-host/src/WebJobs.Script/ExtensionBundle/ExtensionBundleManager.cs : 83
at async Microsoft.Azure.WebJobs.Script.ExtensionBundle.ExtensionBundleManager.GetExtensionBundleBinPathAsync() at /src/azure-functions-host/src/WebJobs.Script/ExtensionBundle/ExtensionBundleManager.cs : 294
at async Microsoft.Azure.WebJobs.Script.DependencyInjection.ScriptStartupTypeLocator.GetExtensionsStartupTypesAsync() at /src/azure-functions-host/src/WebJobs.Script/DependencyInjection/ScriptStartupTypeLocator.cs : 108
```

Related to https://github.com/Azure/azure-functions-host/issues/9364

Start in src/WebJobs.Script/ExtensionBundle/ExtensionBundleManager.cs, especially GetLatestMatchingBundleVersionAsync around lines 225-236, and trace its callers through GetBundle and ScriptStartupTypeLocator. Confirm how request exceptions currently propagate; done means a failed bundle-version request is handled like an unsuccessful response so host startup can continue and the caller can decide what to do.

Written by the indexing model from the issue text.