Add dependabot config for Actions only

Author: MattIPv4

.github/dependabot.yml

@@ -0,0 +1,10 @@
+version: 2
+
+updates:
+  - package-ecosystem: github-actions
+    directory: /
+    schedule:
+      interval: weekly
+
+  # Worker dependencies are not updated by Dependabot as the worker is cloned from an upstream repository.
+  # This repository also has a Dependabot rule defined to dismiss Dependabot alerts from `manifest:worker/package-lock.json`.