Resolve "Add exception so the prep/backport MRs for patch releases never have their milestones updated"

Consider adding documentation to the handbook pages for Triage Operations when creating a new triage policy or triage package:

• https://gitlab.com/gitlab-com/www-gitlab-com/blob/master/source/handbook/engineering/quality/triage-operations/index.html.md

Closes #299 (closed)