Draft: Label migration one-offs for newly formed Group Platform Insights and corresponding categories

What does this MR do and why?

Describe in detail what your merge request does and why.

Relates to Update to slack, labels, and handbook pages to ... (gitlab-org/gitlab#478872)

Update 3 files

• /policies/one-off/relabel_observability_categories.yml
• /policies/one-off/groupo11y_groupPA_to_groupplatform_insights.yml
• /.gitlab/ci/one-off.yml

This MR has label updates for the new groupplatform insights and clean up of previous categories merging of 4 old categories into a single Category:Observability label.

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