Update tw-milestone-plan.md
More changes to the milestone template to reflect:
- Transition Release/Release TW assignment to Phi... (#763 - closed)
- TW group change tasks for Plan/Certify => Plan/... (#767 - closed)
- Transition SaaS Platforms/GitLab Dedicated TW a... (#768 - closed)
Also added monthly routine task for backlog item review to reflect handbook update: gitlab-com/www-gitlab-com!120127 (merged)
Edited by Diana Logan