Limit concurrent pipelines so deployment scripts don't clash

Hi.

I think the option to enable a pipeline to run sequentially (one at a time per pipeline / branch, ordered by the commit date) would be very useful.

That would be useful (essential, even) in cases where one commit results in one deploy.

The way it is today, you can't commit multiple times in a short period of time, or it will result in multiple deploys running at the same time.

The configuration could be like this:

#!yml
image: MY_IMAGE
pipelines:
  branches:
    master:
      sequential: true
      - step:
          script:
            - MY_SCRIPT

or

#!yml
image: MY_IMAGE
pipelines:
  branches:
    master:
      parallel: false
      - step:
          script:
            - MY_SCRIPT

Thanks.