Add Dependabot for GitHub action updates

This will help keep up-to-date any actions that we use.

.github/dependabot.yml

@@ -0,0 +1,8 @@
+# https://docs.github.com/en/code-security/dependabot/dependabot-version-updates/configuration-options-for-the-dependabot.yml-file
+
+version: 2
+updates:
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "monthly"