Add Dependabot config

.github/dependabot.yml

@@ -0,0 +1,42 @@
+version: 2
+
+updates:
+  - package-ecosystem: github-actions
+    directory: /
+    schedule:
+      interval: daily
+      time: "14:30"
+      timezone: Europe/London
+    allow:
+      - dependency-type: all
+    # The actions in triage-issues.yml are updated in the Homebrew/.github repo
+    ignore:
+      - dependency-name: actions/stale
+      - dependency-name: dessant/lock-threads
+    commit-message:
+      prefix: workflows
+
+  - package-ecosystem: bundler
+    directory: /
+    schedule:
+      interval: daily
+      time: "14:30"
+      timezone: Europe/London
+    allow:
+      - dependency-type: all
+    commit-message:
+      prefix: Gemfile.lock
+    groups:
+      security:
+        applies-to: security-updates
+        patterns:
+          - "*"
+      major:
+        applies-to: version-updates
+        update-types:
+          - major
+      minor-patch:
+        applies-to: version-updates
+        update-types:
+          - minor
+          - patch