chore: add drf-lint pre-commit hook with baseline

[blarghmatey]

What are the relevant tickets?

N/A

Description (What does it do?)

Adds the drf-serializer-orm-check pre-commit hook from mitodl/ol-django which uses mitol-drf-lint to detect Django ORM queries inside DRF serializer methods — a common source of N+1 query bugs.

Also generates an initial drf_lint_baseline.json recording all pre-existing violations so the hook only flags new issues going forward. Existing violations can be addressed incrementally.

mitol-drf-lint is added as a dev dependency to support running the tool locally outside of pre-commit.

How can this be tested?

1. Install pre-commit hooks: pre-commit install
2. Modify or create a serializers.py file that calls ORM methods (e.g. .filter(), .get()) inside a serializer method body
3. Attempt to commit — the hook should flag the new violation
4. Alternatively, run directly: uv run drf-lint <path/to/serializers.py>

Additional Context

The baseline was generated with:

uv run drf-lint --generate-baseline --baseline drf_lint_baseline.json $(find . -name "serializers.py" ! -path "*/migrations/*")

To regenerate after fixing existing violations, rerun the above command.