Generate default labels policies and CI jobs

What does this MR do and why?

This allows to define projects and groups where a group's default labels should be applied to all open issues and MRs.

This can be defined in the group-definition.yml file.

Expected impact & dry-runs

No changes expected from an automation point of view. Only better maintenance, and easier contributions.

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:
  • Relevant Slack channels => #eng-managers
  • Engineering week-in-review