chore: configure monthly grouped dependabot updates

Author: fey

.github/dependabot.yml

@@ -0,0 +1,13 @@
+version: 2
+updates:
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "monthly"
+      time: "03:00"
+      timezone: "Etc/UTC"
+    open-pull-requests-limit: 1
+    labels: ["dependencies", "automated"]
+    groups:
+      github-actions-all:
+        patterns: ["*"]