enable dependabot on uno playground (#59)

enable dependabot on uno playground

.dependabot/config.yml

@@ -0,0 +1,9 @@
+version: 1
+update_configs:
+  - package_manager: "dotnet:nuget"
+    directory: "/"
+    update_schedule: "weekly"
+
+    default_labels:
+      - "kind/dependency"
+      - "do-not-merge/work-in-progress"