MM-52438 Clean up web app CI and only run when web app code is changed (#23232)

* MM-52438 Only run web app CI for PRs with web app changes

* MM-52438 Don't wait to run web app tests in CI

* MM-52438 Remove commented out caching

* MM-52438 Reuse steps to set up webapp environment

* MM-52438 Add test-ci script to root package.json

* Simplify path filter

.github/workflows/webapp-ci-master.yml

@@ -5,7 +5,6 @@ on:
       - master
       - cloud
       - release-*
-      - mono-repo*
 
 jobs:
   master-ci: