Implement new `sdk-sync` tool (#1336)

* Copy `smithy-rs-sync` into new `sdk-sync`
* Refactor to use `Git` trait instead of `git2`
* Abstract out gradle commands
* Abstract out filesystem operations
* Add a mocked end to end test
* Load `versions.toml` for revision information
* Sync example commits into one aggregate commit
* Reorganize tests
* Only include smithy-rs commits that change the SDK
* Add `sdk-sync` to Docker build image
* Sync models
* Greatly increase debug logging
* Add git invocation tests
* Fix running in CI detection for Docker build image
* Rename `e2e_test` to `mock_e2e_test`
* Add full E2E test and fix a bug with change detection