Add dependabot for actions

Author: mfitz

.github/workflows/dependabot.yml

@@ -0,0 +1,13 @@
+version: 2
+updates:
+
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "weekly"
+      day: "monday"
+      time: "10:00" # time is in UTC
+    reviewers:
+      - "brynpickering"
+      - "mfitz"
+      - "KasiaKoz"