Add process sections to Monitor stage
This MR adds 4 new sections to the "How to work with Monitor" topic. This is a first step in better documenting our processes for the Monitor Stage. This MR should resolve gitlab-org/monitor/general#22 (closed)
@sarahwaldner @ClemMakesApps @mnohr @adrielsantiago @ameliabauerly @svoegeli - please review!