Optionally prevent running multiple pipelines in parallel

If I push one commit quickly after another to my repository, pipeline starts for each of those commits. Because they start for each of those commits, but each pipeline run takes a long time, they end up running in parallel. This is problematic in my case base some jobs assume that only they are running at a time.

I have not found a way to make the second pipeline start only after the first pipeline finishes, so I would propose that such setting is added.