+ Add config for GH Dependent Bot

https://docs.github.com/en/free-pro-team@latest/github/administering-a-repository/configuration-options-for-dependency-updates
https://github.blog/2020-06-01-keep-all-your-packages-up-to-date-with-dependabot/

Author: PikachuEXE

.github/dependabot.yml

@@ -0,0 +1,20 @@
+version: 2
+updates:
+  - package-ecosystem: bundler
+    directory: "/"
+    schedule:
+      interval: monthly
+      time: "06:00"
+      timezone: Asia/Hong_Kong
+    open-pull-requests-limit: 10
+    labels:
+      - "dependencies"
+  - package-ecosystem: github-actions
+    directory: "/"
+    schedule:
+      interval: monthly
+      time: "06:00"
+      timezone: Asia/Hong_Kong
+    open-pull-requests-limit: 10
+    labels:
+      - "dependencies"