Code Coverage

[BlairCurrey]

Make a time-boxed attempt at adding code coverage from our jest tests. Solution should:

• prefer a local only version if possible, otherwise look into a service like codecov and integrating with github PRs.
• cover backend, auth, and token-introspection jest tests

[BlairCurrey]

The point behind adding code coverage is to be useful insight for developers making changes as needed, and not as some target or CI check. The main ways I envision using it are comparing branch coverage to main as a quick sanity check for test changes or checking that tests on a new feature cover what I think it does. The latter can easily be handled locally by just adding the --coverage flag but I'm less sure about handling the former locally.