infra: add dependabot for github actions (#179)

* infra: add dependabot for github actions

----

Co-authored-by: Coull <accoull@amazon.com>
Co-authored-by: Ryan Shaffer <3620100+rmshaffer@users.noreply.github.com>

.github/dependabot.yml

@@ -0,0 +1,12 @@
+# Set update schedule for GitHub Actions
+
+version: 2
+updates:
+
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      # Check for updates to GitHub Actions every month
+      interval: "monthly"
+    commit-message:
+      prefix: infra