Don't slip past milestones

What does this MR do and why?

This change makes it so that our automation is up-to-date with our documentation for missed milestones.

Open issues and merge requests that have missed the current release will be rescheduled to the next active milestone.

Only apply ~missed:x.y to a resource if the applied milestone was the one that just passed.

Given a backport MR targeting release %17.11 - since current_date is after %17.11 , this automation would have applied missed:17.11, even though this is a backport MR that is specifically intended to target %17.11

Action items

• [-] If adding environment variables for reactive processors, update config/triage-web.yaml and .gitlab/ci/triage-web.yml
• [-] (If applicable) Add documentation to the handbook pages for Triage Operations =>
• (If applicable) Identify the affected groups and how to communicate to them:
  • /cc @person_or_group =>
  • Relevant Slack channels =>
  • Engineering week-in-review