Add support for the collaborator access level/push
    
    Until this commit we only allowed project committer to push to the
    project on dist-git while pagure has gained a few months back a new
    access level: collaborator which allow to give some user access to only
    certain branches.
    
    With this commit we're turning on this feature on dist-git as well.
    
    Fixes https://pagure.io/releng/issue/9834
    
    Signed-off-by: Pierre-Yves Chibon <pingou@pingoured.fr>