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

[relevantsam]

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

• 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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[jdisanti]

Thank you for fixing this!

[relevantsam]

12 | const X_RAY_TRACE_HEADER: HeaderName = HeaderName::from_static("x-amzn-trace-id");

We looked at suppressing the clippy warning and adding a const array. The Vec input for SigningSettings reduces the value for this, so we went with the original approach.