[CI] Add github-actions ecosystem to Dependabot

Group updates to reduce repo noise

Setup to run weekly.

Added 7 day cooldown period

https://docs.github.com/en/code-security/reference/supply-chain-security/dependabot-options-reference

Author: jbampton

.github/dependabot.yml

@@ -22,8 +22,19 @@
 
 version: 2
 updates:
-  - package-ecosystem: "maven" # See documentation for possible values
-    directory: "/" # Location of package manifests
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    open-pull-requests-limit: 2
+    schedule:
+      interval: "weekly"
+    groups:
+      github-actions-dependencies:
+        patterns:
+          - "*"
+    cooldown:
+      default-days: 7
+  - package-ecosystem: "maven"
+    directory: "/"
     schedule:
       interval: "daily"
     cooldown: