Add a new API endpoint to update the options set for a project
    
    The idea is to use the new endpoint to retrieve the current options,
    adjust the options of interest and then use this endpoint to update them
    in pagure.
    
    Fixes https://pagure.io/pagure/issue/3892
    
    Signed-off-by: Pierre-Yves Chibon <pingou@pingoured.fr>