Add monthly grouped Dependabot updates (#6)

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>

Author: Copilot

.github/dependabot.yml

@@ -0,0 +1,19 @@
+version: 2
+updates:
+  - package-ecosystem: gomod
+    directory: /
+    schedule:
+      interval: monthly
+    groups:
+      go-dependencies:
+        patterns:
+          - "*"
+
+  - package-ecosystem: github-actions
+    directory: /
+    schedule:
+      interval: monthly
+    groups:
+      github-actions:
+        patterns:
+          - "*"