chore: add dependabot config (#7)

cloudflare-worker/.github/dependabot.yml

@@ -0,0 +1,19 @@
+version: 2
+updates:
+  - package-ecosystem: "npm"
+    directory: "/"
+    schedule:
+      interval: "weekly"
+    open-pull-requests-limit: 10
+    groups:
+      minor-and-patch:
+        update-types: ["minor", "patch"]
+      security:
+        applies-to: security-updates
+        patterns: ["*"]
+    versioning-strategy: increase
+    labels: ["dependencies", "security"]
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "monthly"