Switch default Git auth backend to the 'pagure_authorized_keys' backend
    
    The Gitolite backend has turned into a rather difficult backend to support
    by default. Among other things, newer versions of Gitolite seem to have
    issues with parsing the configuration data generated by Pagure.
    
    Combined with the performance issues for larger setups and the complexity
    required to set up Pagure correctly with the Gitolite backend, it makes
    sense to switch the default backend to the simpler, internal one.
    
    Signed-off-by: Neal Gompa <ngompa13@gmail.com>