Allow manually triggering prometheus rules check

Author: mkuratczyk

.github/workflows/prometheus-rules.yml

@@ -1,8 +1,10 @@
 name: "Prometheus Rules"
 on:
+  workflow_dispatch:
   push:
     branches:
     - main
+    - add-promtool
     paths:
     - observability/prometheus/rules/**/*.y*ml