How may I limit the concurrency level of pipelines executions to 1 across all branches ?
Current behavior:
Whenever new commits are pushed to a branch, as long as there is no `[skip ci]` in the commit message, a pipeline execution would start immediately. Because the pipeline script uses some external resources, multiple pipelines running at the same time will crash each other.
Desired behavior:
After new commits pushed, the pipeline execution is queued and started after all other executions complete.
