[CI] Archive build reasons (elastic#21347)

Jenkinsfile

@@ -105,18 +105,11 @@ pipeline {
  mapParallelTasks["${k}"] = v
  }
  }
+ notifyBuildReason()
  parallel(mapParallelTasks)
  }
  }
  }
- post {
- always {
- dir("${BASE_DIR}"){
- // Archive the markdown files that contain the build reasons
- archiveArtifacts(allowEmptyArchive: false, artifacts: 'build-reasons/*.md')
- }
- }
- }
  }
  }
  post {
@@ -588,6 +581,17 @@ def isDockerInstalled(){
  }
 }
 
+/**
+* Notify the build reason.
+*/
+def notifyBuildReason() {
+ // Archive the build reason here, since the workspace can be deleted when running the parallel stages.
+ archiveArtifacts(allowEmptyArchive: true, artifacts: 'build-reasons/*.*')
+ if (isPR()) {
+ echo 'TODO: Add a comment with the build reason (this is required to be implemented in the shared library)'
+ }
+}
+
 /**
 * This class is the one used for running the parallel stages, therefore
 * its arguments are passed by the beatsStages step.