Move Plan team page to correct place
Review app: https://refs-merge-requests-21936-head.about-src.gitlab.com/handbook/engineering/development/dev/plan/
Two commits:
- Move the Plan team page to the right place, update CODEOWNERS, fix broken links, etc.
- Update the team page template to include hiring charts.
Part of #3940 (closed).
Edited by Sean McGivern