Enable zot apikey extension for key management UI

The auth.apikey flag enables *using* API keys but the extensions.apikey
section is needed for the UI to show login and key generation options.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

ansible/roles/zot/templates/config.json.j2

@@ -38,7 +38,7 @@
           "anonymousPolicy": ["read"],
           "defaultPolicy": ["read"]
         }
-      }
+      },
     }
   },
   "log": {
@@ -73,6 +73,9 @@
     },
     "ui": {
       "enable": true
+    },
+    "apikey": {
+      "enable": true
     }
   }
 }