Update Monitor team members organization to prepare for group split

Matt Nohrrequested to merge
monitor-people-organize into master

As we updated our team information to prepare for the group split, all the monitor team members ended up in the Stable Counterparts section and we had empty Backend and Frontend lists on the Monitor Group page /handbook/engineering/ops/monitor/

I updated the page to have this structure with the correct people in each list:

Backend Team members
  Debugging & Health
  APM
Frontend Team members
Stable counterparts
Edited by Matt Nohr

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