Merge #2561

2561: Add dependabot for GHA r=Kerollmops a=curquiza

No panic, I only add dependabot to update our CI, not the rust dependencies. Indeed, no easy command exists for this.
If it's too much regular notification, as usual, I will remove it.

Co-authored-by: Clémentine Urquizar <clementine@meilisearch.com>

.github/dependabot.yml

@@ -0,0 +1,9 @@
+# Set update schedule for GitHub Actions only
+
+version: 2
+updates:
+
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "monthly"