Allows site admins to view all repositories
Created by: beyang
Previously, they were subject to authz checks just like every other user. This didn't make sense, because site admins must have the ability to enable/disable any repository. Fixes #660 (closed) and #675 (closed).
This PR does not need to update the CHANGELOG because this behavior has not yet shipped.
Post-merge TODO
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Cherry-pick to 2.13