feat: Enable StsWebIdentityCredentialsProvider to be given a custom httpClient

[sroze]

This enables to provide a custom SdkHttpClient to the web identity token file provider.

Motivation and Context

Running a Quarkus application in EKS, the application authenticates itself to AWS services with the WebIdentityTokenFileCredentialsProvider. For some reason, I can't get Quarkus to recognise the available HTTP client when built with the "native" profile so have to explicitly given the httpClient to the AWS clients. However, it doesn't work with this authentication provider because we can't give it our own HTTP client.

Description

This allows to pass down the httpClient from WebIdentityTokenFileCredentialsProvider to the STS client.

Testing

• TODO.

Screenshots (if appropriate)

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)

Checklist

• I have read the CONTRIBUTING document
• Local run of mvn install succeeds
• My code follows the code style of this project
• My change requires a change to the Javadoc documentation
• I have updated the Javadoc documentation accordingly
• I have read the README document
• I have added tests to cover my changes
• All new and existing tests passed
• A short description of the change has been added to the CHANGELOG
• My change is to implement 1.11 parity feature and I have updated LaunchChangelog

License

• I confirm that this pull request can be released under the Apache 2 license

[debora-ito]

@sroze This PR has been in draft state for some time now, do you still want to proceed?

[github-actions]

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