Allow to stop pipeline from MR widget

Sometimes, in a MR, I know that the pipeline will fail, or there's no use in running it and I forgot to add [ci skip] to the commit, so I want to stop it.

In order to stop it, I have to open the pipelines tab, although I have the pipeline in the MR widget.

It would save me a click if we could stop the pipeline from the mr widget

/cc @jlenny @dimitrieh