[Test Proxy] Sanitize OAuth requests/responses throughout SDK by default

[mccoyp]

Description

OAuth interactions are a major potential source of test principal secret leakage if client data isn't correctly sanitized elsewhere. Since these interactions aren't necessary for any tests that I'm aware of, and sanitizing them won't break any existing functionality, this updates the test proxy's startup code to automatically register the OAuth response sanitizer, thereby opting everyone in to sanitizing them.

All SDK Contribution checklist:

• The pull request does not introduce [breaking changes]
• CHANGELOG is updated for new features, bug fixes or other significant changes.
• I have read the contribution guidelines.

General Guidelines and Best Practices

• Title of the pull request is clear and informative.
• There are a small number of commits, each of which have an informative message. This means that previously merged commits do not appear in the history of the PR. For more information on cleaning up the commits in your PR, see this page.

Testing Guidelines

• Pull request includes test coverage for the included changes.

[mccoyp]

/azp run python - storage - ci

[azure-pipelines]

Azure Pipelines could not run because the pipeline triggers exclude this branch/path.

[mccoyp]

Storage CI run: https://dev.azure.com/azure-sdk/public/_build/results?buildId=3620094&view=results ✅
ML CI run: https://dev.azure.com/azure-sdk/public/_build/results?buildId=3620085&view=results ✅
Identity CI run: https://dev.azure.com/azure-sdk/public/_build/results?buildId=3620925&view=results ✅