Add dependabot cooldowns

- Added cooldown period for bundler(3 days) and github-actions(3 days) as per the documentation - https://docs.publishing.service.gov.uk/manual/manage-dependencies.html#example-configurations

Author: sairamya93

.github/dependabot.yml

@@ -4,7 +4,15 @@ updates:
     directory: /
     schedule:
       interval: daily
+    cooldown:
+      default-days: 3
+      exclude:
+        - gds-api-adapters
+        - govuk_*
+        - rubocop-govuk
   - package-ecosystem: github-actions
     directory: /
     schedule:
       interval: daily
+    cooldown:
+      default-days: 3