chore(.github): group dependabot PRs and reduce frequency (#499)

Author: mafredri

.github/dependabot.yml

@@ -1,9 +1,24 @@
 version: 2
 updates:
+  # Track in case we ever add dependencies.
+  - package-ecosystem: 'gomod'
+    directory: '/'
+    schedule:
+      interval: 'weekly'
+    commit-message:
+      prefix: 'chore'
+
+  # Keep example and test/benchmark deps up-to-date.
   - package-ecosystem: 'gomod'
     directories:
-      - '/'
       - '/internal/examples'
       - '/internal/thirdparty'
     schedule:
-      interval: 'weekly'
+      interval: 'monthly'
+    commit-message:
+      prefix: 'chore'
+    labels: []
+    groups:
+      internal-deps:
+        patterns:
+          - '*'