CI: Add unified Jenkinsfile for all test pipelines
This MR introduces a single Jenkinsfile to cover all current CI test pipelines
Improvements:
- correct reporting of the start timestamp in the HTML report
- harmonize log collection - always collect as test_logs_${env.BUILD_ID}.zip
Next step (follow-up MR):
- once this new Jenkinsfile is tested and validated in CI, we can remove existing Jenkinsfiles used in CI pipelines (except Jenkinsfile-GitLab-Container, Jenkinsfile-push-registry, Jenkinsfile-colosseum)
Test runs:
Edited by Jaroslava Fiedlerova