Exclude transfer-encoding header from sigv4(a) signing

[landonxjames]

Add changelog

Motivation and Context

Exclude transfer-encoding header from sigv4(a) signing. It is a hop by hop header and can be erased or modified by a proxy (in our particular case Cloudfront)

Description

Testing

Updated the existing tests for excluded headers.

Checklist

• For changes to the AWS SDK, generated SDK code, or SDK runtime crates, I have created a changelog entry Markdown file in the .changelog directory, specifying "aws-sdk-rust" in the applies_to key.

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[ysaito1001]

LGTM. Existing integration tests for S3 capture the transfer-encoding header but I suspect they won't be broken since the way they verify expected results in tests is resilient to the changes in PR.

I am ok with leaving the transfer-encoding in connection recording tests; if we can create an issue for cleanup, that'd be great but keeping it around wouldn't be a blocker (please ignore that since the transfer-encoding in connection recording tests only appear in responses). Maybe want to quickly check (e.g., by using capture_request) that the transfer-encoding header is indeed excluded from an outgoing request.

[github-actions]

A new generated diff is ready to view.

• AWS SDK (ignoring whitespace)
• No codegen difference in the Client Test
• No codegen difference in the Server Test
• No codegen difference in the Server Test Python
• No codegen difference in the Server Test Typescript

A new doc preview is ready to view.

[landonxjames]

Existing integration tests for S3 capture the transfer-encoding header but I suspect they won't be broken since the way they verify expected results in tests is resilient to the changes in PR.

Looks like all of those should be able to stay since all of them appear in a Response and this change only impacts request signing. None of the SignedHeaders values reference transfer-encoding