Add clusterRef to BindTSIGKey

TSIG keys were included in every cluster's keys.conf namespace-wide. When
multiple clusters share a namespace, that leaks keys across clusters. Add
spec.clusterRef so a key can target a specific BindCluster; empty keeps
the shared (all-clusters-in-namespace) behaviour.

- api: BindTSIGKey.spec.clusterRef (optional)
- BindCluster keys.conf now includes only keys with matching or empty
  clusterRef
- regenerate CRDs + install.yaml bundle

config/crd/bases/bind.unkin.net_bindtsigkeys.yaml

@@ -66,6 +66,12 @@ spec:
                 - hmac-sha1
                 - hmac-md5
                 type: string
+              clusterRef:
+                description: |-
+                  ClusterRef names the BindCluster this key is included in. When empty the
+                  key is shared with every cluster in the namespace (useful when multiple
+                  clusters share one namespace).
+                type: string
               importExisting:
                 description: |-
                   ImportExisting, when true, means the referenced Secret already contains a

config/crd/install.yaml

@@ -2043,6 +2043,12 @@ spec:
                 - hmac-sha1
                 - hmac-md5
                 type: string
+              clusterRef:
+                description: |-
+                  ClusterRef names the BindCluster this key is included in. When empty the
+                  key is shared with every cluster in the namespace (useful when multiple
+                  clusters share one namespace).
+                type: string
               importExisting:
                 description: |-
                   ImportExisting, when true, means the referenced Secret already contains a