Initial CRD handling

[k15r]

Implement as two independent PRs:

• Implement NATS CRD based on design proposal

• Implement Validation

  • test if CEL-Validation is available in k8s v1.25
    - [ ] if not, use Admission control webhook (validating webhook)
    • if yes, use CEL-Validation
  • add validation of memSorage: dont allow enable=10 if size=0 and vice versa
  • add validation of fileStorage: make immutable if once set
  • add validation for cluster.size to only accept numbers odd numbers > 0

• Implement defaulting

• talk to team; what about the validation of resources for SLA compliance?

followup: #68

[mfaizanse]

@friedrichwilken Does this PR cover the 2nd AC Admission control webhook (validating webhook)?

[friedrichwilken]

@mfaizanse no, as the original task says: Implement as two independent PRs,
there will be a second PR for that (that I am working on right now.)

[k15r]

Blocked until checked if validation rules can be used

[friedrichwilken]

To unblock this, check if validation rules can be used in gardener on a 1.25 cluster.

[friedrichwilken]

I used this tutorial to validate that the CEL-validation is working: CEL-tutorial