refactor: consolidate CEL filter into ShootSelector struct

[mikolajkucinski]

Summary

• Consolidated shootSelector and shootFilter into a single shootSelector struct with labelSelector and expression fields
• CEL filtering now happens at the watch level via predicates instead of in the reconcile loop
• CEL-excluded shoots are tracked in status.shoots with Excluded status alongside onboarded/failed shoots
• Label selector now uses LabelSelectorAsSelector to support both matchLabels and matchExpressions
• Renamed ClusterStatus to ShootStatus with Enum=Onboarded;Failed;Excluded
• Renamed status.clusters to status.shoots and status.totalShootCount to status.totalTargetShootCount
• CEL filter errors emit warning events on the CareInstruction

Breaking change: shootSelector field structure changed

Migrate existing CareInstructions with

kubectl get careinstructions -A -o json | \
  jq -c '.items[] |
    .spec.shootSelector = ({
      labelSelector: .spec.shootSelector,
      expression: .spec.shootFilter
    } | del(.[] | nulls)) |
    del(.spec.shootFilter)' | \
  while read -r ci; do
    echo "$ci" | kubectl apply -f -
  done

[uwe-mayer]

Some suggestions on status collection, nice work!

[uwe-mayer]

One comment on the code I initialy wrote. I think I returned too early on error. Can you take a 2nd look?

[github-actions]

Merging this branch will not change overall coverage

Impacted Packages	Coverage Δ	🤖
github.com/cloudoperators/shoot-grafter/api/v1alpha1	0.00% (ø)
github.com/cloudoperators/shoot-grafter/controller/careinstruction	0.00% (ø)
github.com/cloudoperators/shoot-grafter/controller/shoot	0.00% (ø)
github.com/cloudoperators/shoot-grafter/webhook/v1alpha1	0.00% (ø)

---

Coverage by file

Changed files (no unit tests)

Changed File	Coverage Δ	Total	Covered	Missed	🤖
github.com/cloudoperators/shoot-grafter/api/v1alpha1/careinstruction_types.go	0.00% (ø)	0	0	0
github.com/cloudoperators/shoot-grafter/api/v1alpha1/zz_generated.deepcopy.go	0.00% (ø)	0	0	0
github.com/cloudoperators/shoot-grafter/controller/careinstruction/careinstruction_controller.go	0.00% (ø)	0	0	0
github.com/cloudoperators/shoot-grafter/controller/shoot/shoot_controller.go	0.00% (ø)	0	0	0
github.com/cloudoperators/shoot-grafter/webhook/v1alpha1/careinstruction_webhook.go	0.00% (ø)	0	0	0

Please note that the "Total", "Covered", and "Missed" counts above refer to code statements instead of lines of code. The value in brackets refers to the test coverage of that file in the old version of the code.

Changed unit test files

• github.com/cloudoperators/shoot-grafter/controller/careinstruction/careinstruction_controller_test.go
• github.com/cloudoperators/shoot-grafter/controller/shoot/shoot_controller_test.go