[FEAT shoot-grafter] - Watch AuthenticationConfig CM changes

[uwe-mayer]

Priority

(Medium) I'm annoyed but I'll live

Description

Currently the shoot_controller only watches Shoots on the garden API.
We want to also reconcile on AuthenticationConfiguration CM changes.
For this we need to label the CMs managed by shoot-grafter with the respective
shoot-grafter.cloudoperators.dev/careinstruction: <ci-name> on first interaction/creation.

Acceptance criteria

• AuthenticationConfiguration CMs are labelled by shoot_controller with shoot-grafter.cloudoperators.dev/careinstruction: <ci-name> on first interaction (either creation or update of existing)
• shoot_controller reconciles Shoots when auth CMs change
• Behavior is validated via tests
• Docs are updated (small note)

Reference Issues

No response