make renovate configs more restrictive in their scope

apps/immich/renovate.json

@@ -7,4 +7,4 @@
       "groupSlug": "immich-app-images"
     }
   ]
-  }
+}

infrastructure/external-dns/renovate.json

@@ -8,6 +8,7 @@
   "packageRules": [
     {
       "matchDatasources": ["docker"],
+      "matchPackageNames": ["git.kluster.moll.re/remoll/dns"],
       "versioning": "regex:^(?<major>\\d+)\\.(?<minor>\\d+)\\.(?<patch>\\d+)-build.(?<build>\\d+)$"
     }
   ]