Add a tool `sdk-lockfiles` to audit lockfiles (#3827)

## Motivation and Context
See
[README](https://github.com/smithy-lang/smithy-rs/blob/b9f363352603a14305a7cf7ca0317eaf431f638e/tools/ci-build/sdk-lockfiles/README.md)

A later PR will use this tool to enforce the check (likely during the
execution of pre-commit-hooks).

## Testing
- Added unit tests for the tool
- Ran the tool against currently checked-in lockflies in the `main`
branch and ensured the SDK lockfile contained dependencies listed in the
other runtime lockfiles.

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