Implement method to fetch groups on which user has a specified access level, whether directly or indirectly

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There isn't currently an easy way to find out which groups a user has access to with a certain access level. This exists for projects, with User#authorized_projects, but User#authorized_groups doesn't support specifying an access level. This is currently causing a bug where the runners returned by the Runner REST endpoints don't return runners belonging to groups where the user is indirectly a maintainer.