here is the snippet 
Now what I want to do is instead of blindly running the pipeline, wait until the pull request is approved.
Quite alot of times after a PR is created, so many changes are required, and pipelines are running for no purpose. and best way to avoid that is only after the "merge" button is clicked.
current flow
Create PR -> Run Pipeline & Code Review -> Press Merge -> Merge
wanted flow
Create PR -> Code Review -> Press Merge -> Run Pipeline -> Merge