chore(test): add `reason` field to node compat test config (#30469)
This was done so we can show it later on `node-test-viewer`.
Other notable changes:
- Move ignored test list from `run_all_test_unmodified.ts` to
`config.toml`
- Add `parallel/test-os-checked-function.js` to the ignore list
- Adjust the `README.md`