Ability to specify AWS config profile name as source for credentials

## What?

It should be possible to specify the AWS config profile name used to source credentials (per archive backend, per AWS input, etc.).

## Why?

Being able to specify different profiles in different places would be beneficial when it's not convenient to set up role assumption, but multiple principals need to be used (and use of long-term credentials is not desirable).

Unlike other "automatic" AWS credential sources (e.g. environment variables), there may be multiple profiles defined in the AWS config.

* https://github.com/Graylog2/graylog2-server/blob/6.1.8/graylog2-server/src/main/java/org/graylog/integrations/aws/AWSAuthFactory.java
* https://docs.aws.amazon.com/sdk-for-java/latest/developer-guide/credentials-chain.html
* https://sdk.amazonaws.com/java/api/latest/software/amazon/awssdk/auth/credentials/ProfileCredentialsProvider.html

## Your Environment

* Graylog Version: `6.1.8`