Ability to stop runs

[yebrahim]

This requires both the backend support work, an API, and a frontend button to call the API.
@Ark-kun has done some work to explore using Argo's activeDeadlineSeconds field. We also need proper messaging to set the user's expectations that this will stop the workflow without ability to resume.

@Ark-kun, if I understand correctly, this will terminate all the workflow's pods too, not just stop scheduling new ones, correct?

@ajayalfred we'll need a spec and messaging around this experience.

[ajayalfred]

Copy. I'll get this to you asap.

[rileyjbauer]

This functionality is available as of #1039.

Note that for Pipelines that start jobs in GCP, such as those using DataProc, the termination of the pipeline results in a best effort attempt to stop running jobs as soon as possible.
For example, I ran this notebook twice:
https://github.com/kubeflow/pipelines/tree/master/components/gcp/dataproc/submit_hive_job
and the first time I terminated it, the hive query was stopped. The second time, I terminated the pipeline (so the UI showed it as terminated), but the hive query completed before the "cancel" command reached it.

This behavior should be documented to avoid surprising users.