Provide support for defining more granular authorizations for our future Perf sheriffs. Presumably, they'll share various skills & experience levels so they can't be simply granted access to everything on Perfherder/TaskCluster.
For start, just implement 2 ranks:
- community level rank, with very low access (barely more than public read access; will definitely lack retrigger/backfill on TaskCluster, as that requires Commit Access Level 3)
- full access rank, similar to what me/bebe/jmaher/davehunt etc already have