Move ApplyUserAgentStage to later stage in request pipeline

Motivation and Context

Currently facing issue in few stages (like CompressRequestStage and HttpChecksumStage) where business metrics are recorded after User-Agent is finalized, causing metrics to not appear in the header. Moving ApplyUserAgentStage later in the pipeline will eliminate this issue.

Modifications

Moved ApplyUserAgentStage to execute after HttpChecksumStage in the request pipeline in AmazonSyncHttpClient and AmazonAsyncHttpClient.

Testing

• Checked all the existing tests are passing.

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 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