3rd party repos policy: abstract the diverse repos clause
    
    The policy states that 3rd party repos shouldn't include "diverse
    repos". The principle here is that Fedora should retain control
    of the software that's being made available, as opposed to
    enabling repos that are out of our control and whose behaviour
    is risk-prone.
    
    It is helpful to restate this "diverse repos" clause in a more
    generic manner, in order to enable other mechanisms for managing
    3rd party repos, while remaining true to the intent of the policy.
    
    For example, a working group could use a whitelist to control
    which software is made available from a larger repository.