Add dependabot monthly GHA autoupdate config

Author: mfisher87

.github/dependabot.yml

@@ -0,0 +1,17 @@
+version: 2
+updates:
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "monthly"
+    cooldown:
+      default-days: 7
+    ignore:
+      - dependency-name: "*"
+        update-types:
+          - "version-update:semver-minor"
+          - "version-update:semver-patch"
+    groups:
+      gha-dependencies:
+        patterns:
+          - "*"