Label Community Contribution MRs for the about.GitLab.com website

• Check the author is not a member of the gitlab-com group
• Label
  • Community Contribution
  • Website
• Mention
  • @gl-website
• Add a comment for the author to see

Currently the rule will be limited to the updating the latest 20 MRs per run, but we can run this on a daily basis

TODO:

• Create scheduled pipeline
• Activate scheduled pipeline

Closes #115 (closed)