Make external-dns tier authoritative (drop dynamic mode)

The dynamic cluster mode was removed from the operator; RFC2136 update
capability is a per-zone property, not a cluster role. The external-dns
tier is an authoritative cluster whose zones set dynamicUpdate.

- switch binddns-externaldns BindCluster to mode authoritative
- regenerate bindcluster schema (enum: authoritative, resolver)

schemas/bind.unkin.net/bindcluster_v1alpha1.json

@@ -682,8 +682,7 @@
           "default": "authoritative",
           "enum": [
             "authoritative",
-            "resolver",
-            "dynamic"
+            "resolver"
           ],
           "type": "string"
         },