Add policy to automatically set milestone on workflow items

What does this MR do and why?

Add 4 different hygiene policies for workflow cleanup.

1. Open issues with workflowin dev or later will be added to the current milestone
2. Open issues without a milestone and workflowready for development will be moved to workflowplanning breakdown
3. Issues in the current milestone with workflowplanning breakdown will be bumped to the next milestone
4. Issues in future milestones with no workflow labels will have workflowplanning breakdown applied

Turn this on for the gitlab-org/gitaly and gitlab-org/git projects.

fixes: gitlab-org/gitaly#5454 (closed)

Expected impact & dry-runs

These are strongly recommended to assist reviewers and reduce the time to merge your change.

See https://gitlab.com/gitlab-org/quality/triage-ops/-/tree/master/doc/scheduled#testing-policies-with-a-dry-run on how to perform dry-runs for new policies.

See https://gitlab.com/gitlab-org/quality/triage-ops/-/blob/master/doc/reactive/best_practices.md#use-the-sandbox-to-test-new-processors on how to make sure a new processor can be tested.

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