chore[docs]: document committers and maintainers in CONTRIBUTING

[lwwmanning]

For public legibility. This is just a port from the existing PCC / permissions structure.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 84.80%. Comparing base (69ef61d) to head (d6f73ae).
⚠️ Report is 11 commits behind head on develop.

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