Expand skipped headers for sigv4 canonical request signing to include...

Expand skipped headers for sigv4 canonical request signing to include x-amzn-trace-id and authorization headers. (#2815)

## Motivation and Context
When customers add x-ray headers to requests, the SigV4 signer should
exclude them, or the generated canonical signature will not match the
remote service's, since many services being called are written with
non-rust SDKs that automatically exclude these common headers.

The Rust SDK should exclude a similar set of headers to the other
popular AWS SDKs. While this is not uniform across the SDKs, a minimal
set should be excluded and others should be considered to be excluded in
future PRs.

## Description

* Expands the set of headers excluded from canonical request calculation
to include "x-amzn-trace-id" and "authorization" (since authorization
will be added as a part of this process).

## Testing

* Added headers to exclusion test & validated with `cargo test`
* `./gradlew :aws:sdk:test`  

## Checklist
- [x] I have updated `CHANGELOG.next.toml` if I made changes to the AWS
SDK, generated SDK code, or SDK runtime crates

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Co-authored-by: Sam Bartlett <sbartl@amazon.com>
Co-authored-by: Zelda Hessler <zhessler@amazon.com>