feat(tenant): add available classes as status fields

[oliverbaehler]

Adds all the available classes as status for a tenant, something like this:

---
apiVersion: capsule.clastix.io/v1beta2
kind: Tenant
metadata:
  creationTimestamp: "2025-11-19T12:55:01Z"
  generation: 1
  labels:
    kubernetes.io/metadata.name: e2e-runtime-no-restrictions
  name: e2e-runtime-no-restrictions
  resourceVersion: "113076"
  uid: 8193f24c-7aa5-49a5-b9eb-d4685c01004e
spec:
  cordoned: false
  gatewayOptions: {}
  ingressOptions:
    hostnameCollisionScope: Disabled
  limitRanges: {}
  networkPolicies: {}
  owners:
  - clusterRoles:
    - admin
    - capsule-namespace-deleter
    kind: User
    name: e2e-gateway-no-restrictions
  preventDeletion: false
  resourceQuotas:
    scope: Tenant
status:
  classes:
    priority:
    - system-cluster-critical
    - system-node-critical
    runtime:
    - customer-containerd
    - customer-runu
    - customer-virt
    - default-runtime
    - disallowed
    - legacy
    storage:
    - standard

This makes the mapping to classes no longer invisible and allows for more complex aggregations at admission.

If no selection is made (for any class) all cluster resources are shown (user must handle this via labels at best).

Fixes #1744