New command `disable-monitoring`
    
    After the repository is retired, its monitoring needs to be disabled.
    
    Based also on the code from @lenkaseg:
    https://pagure.io/fedpkg/pull-request/497
    https://pagure.io/rpkg/pull-request/646
    
    Relates: https://pagure.io/releng/issue/10724
    JIRA: RHELCMP-11025
    
    Signed-off-by: Ondrej Nosek <onosek@redhat.com>