Trigger PipelineRun on opening/closing PR

Currently PipelinRuns targeting the pull_request event are triggered every time a commit occurs on a pull_request. However, we'd like to be able to trigger a PipelineRun only when a PR is opened or closed and no longer on the commits to the pull request.
One way to achieve this behavior is to use GitHub workflows to start the PipelineRun by sending a CURL request (https://pipelinesascode.com/docs/guide/incoming_webhook/). Unfortunately, we can't set the branch name to any name, since the Repository resource doesn't allow wildcards for the incoming target branch name and constantly updating the Repository resource is not favorable.

Would it be possible to either support wildcards for the incoming target branch name in the Repository resource, or to extend the events or cel expressions to include events for opening/closing PRs?

Start with the incoming webhook documentation linked in the issue and the Repository resource behavior for incoming target branch names. Determine whether the change should support wildcard branches or expose pull-request opening and closing events in event or CEL handling; done means one of these behaviors is supported without repeatedly updating the Repository resource.