ci(github): add dependabot config

- add dependabot config file
- ignore DangerJS dependecies from dependabot

.github/dependabot.yml

@@ -0,0 +1,12 @@
+version: 2
+updates:
+  - package-ecosystem: "all"
+    directory: "/"
+    schedule:
+      interval: "weekly"
+    ignore:
+      - directory: ".gitlab/dangerjs"
+        patterns:
+          - "package-lock.json"
+    # Disable "version updates" (keep only "security updates")
+    open-pull-requests-limit: 0