CE port for pipelines for external pull requests
Detect if pipeline runs for a GitHub pull request When using a mirror for CI/CD only we register a pull_request webhook. When a pull_request webhook is received, if the source branch SHA matches the actual head of the branch in the repository we create immediately a new pipeline for the external pull request. Otherwise we store the pull request info for when the push webhook is received. When using "only/except: external_pull_requests" we can detect if the pipeline has a open pull request on GitHub and create or not the job based on that.