Add default labels to gitlab-ui

This will add ~"devops::ecosystem" and groupfoundations to the opened issues & MRs in the gitlab-org/gitlab-ui project, when there's not already a stage or group label.

Expected impact

Based on the dry-run, this would already add the labels to 370 issues and 4 MRs.

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 =>
  • Week-in-review