Draft: One-off policy to rename webhooks label

What does this MR do and why?

Replace and remove ~"Integration::webhooks" with Category:Webhooks.

Webhooks is not an integration, but a category/functionality.

Related https://gitlab.com/gitlab-org/manage/integrations/team/-/issues/158.

Expected impact & dry-runs

• GitLab.org https://gitlab.com/gitlab-org/quality/triage-ops/-/jobs/3373826517
  • ✅ 19 epics, aligned with expectations. Epics list
  • ✅ 602 issues, aligned with expectations. Issues list
  • ✅ 175 merge requests, aligned with expectations. Merge requests list

Reference:

• https://gitlab.com/gitlab-org/quality/triage-ops/-/tree/master/doc/scheduled#one-off-policies
• https://gitlab.com/gitlab-org/quality/triage-ops/-/tree/master/doc/scheduled#testing-with-a-dry-run

Action items

• (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