Configure Dependabot

- Update less frequently from daily to monthly
- Limit the number of pull requests

Author: ybiquitous

.github/dependabot.yml

@@ -1,7 +1,10 @@
 version: 2
 updates:
-  - package-ecosystem: 'npm'
+  - package-ecosystem: npm
     directory: '/'
     schedule:
-      interval: 'daily'
+      interval: montly
     versioning-strategy: increase
+    open-pull-requests-limit: 1
+    labels:
+      - 'pr: dependencies'