[FEAT shoot-grafter] - Delete clusters when Shoot is deleted

[uwe-mayer]

Priority

None

Description

The current statement in Shoot-grafter Readme is that we do not clean up clusters .
We want to enhance that behaviour and delete Greenhouse Clusters if the respective Shoot no longer exists.
Behavior should stay as is for label matchers

Acceptance Criteria

• When a shoot is deleted on the Garden API the Greenhouse Cluster is deleted:
  • Deleted means 404 on a previously existing shoot Cluster
• We keep the cluster in CareInstruction.Status.Shoots with status=deleted
• Event is emmited
• Tests validate the behaviour
  • Remove shoot - Cluster deleted
  • have a failing request to the Garden API for this should - Cluster is not deleted
• Docs are updated

Reference Issues

Currently blocked by: cloudoperators/greenhouse#1947

[uwe-mayer]

Get 404 on Garden API:

• Delete Cluster
  Need CI status cleanup.

follow-up: Disallow deletion of shoot-grafter owned Cluster resources

follow-up: Shoot-label change, report in CI status and as metric to be alerted on.