Add a new decorator checking that either PR or issues are enabled
    
    This is needed for updating, editing or deleting tags. Issue tracking
    may be disabled for the project but PRs not and thus we need to keep
    tag-related actions available to the project.
    
    Fixes https://pagure.io/pagure/issue/4204
    
    Signed-off-by: Pierre-Yves Chibon <pingou@pingoured.fr></pingou@pingoured.fr>