Add check for SRA codepath to HttpChecksumStage

[haydenbaker]

Motivation and Context

• Since the new signers handle flexible-checksums and aws-chunk coding for unsigned and signed payload cases, we don't need the duplicate logic in HttpChecksumStage
• However, we still need to support the old path when we are not using new signers

Modifications

• Add a condition to check if we are using new SRA code, and return early if we are

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 added tests to cover my changes
• All new and existing tests passed
• I have added a changelog entry. Adding a new entry must be accomplished by running the scripts/new-change script and following the instructions. Commit the new file created by the script in .changes/next-release with your changes.
• 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

[zoewangg]

So we'll still need to keep this class to add md5 checksum header (after SRA is fully released)?

[haydenbaker]

I think so. It appears this behavior was originally in an interceptor: https://github.com/aws/aws-sdk-java-v2/blob/78d2897f73734113071915a56bbdba78add4d5a6/core/sdk-core/src/main/java/software/amazon/awssdk/core/internal/interceptor/HttpChecksumRequiredInterceptor.java

So we either add that interceptor back or keep this stage.

It seems we still need trailer logic from this class, so we probably need to move trailer method up before SRA check

[zoewangg]

Close in favor of #4503