[Feature Request]: Support custom AWS credentials providers

### What would you like to happen?

Currently only a subset of AWS credentials providers is supported by Beam, in some cases support is only available partially. All of the de-serializers are implemented in AwsModule. Users cannot add support for new providers, nor customize support for existing ones.

It would be helpful to support that, e.g. by registering custom implementations via a `AutoService` (similar to `PipelineOptionsRegistrar` or others).

### Issue Priority

Priority: 3 (nice-to-have improvement)

### Issue Components

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