Add npm dependabot (#3210)

Like mentioned
[there](https://github.com/MichMich/MagicMirror/pull/3207#issuecomment-1736181753)

I open an PR with npm dependabot (every monthly)

It might be interesting to have an overview every month

---------

Co-authored-by: Veeck <github@veeck.de>

.github/dependabot.yaml

@@ -5,3 +5,9 @@ updates:
     schedule:
       interval: "weekly"
     target-branch: "develop"
+
+  - package-ecosystem: "npm"
+    directory: "/"
+    schedule:
+      interval: "monthly"
+    target-branch: "develop"