Restrict Redmine Gantt access
    
    - The Gantt PNG export (which includes the Gantt web view) is currently broken, block
      to reduce long error outputs from filling up the log for every request:
      https://progress.opensuse.org/issues/181934
    - Gantt is generally expensive, align restrictions with repository paths.
    
    Once the first issues is resolved, the rules can be consolidated again.
    The individual matching is to allow logged in users to still benefit
    from PDF Gantts.
    
    Signed-off-by: Georg Pfuetzenreuter <mail@georg-pfuetzenreuter.net>