Define a Variable for ID of user running the workflow

[sabreensalama]

Hello,
I have a lot of developers and testers and they are running the workflows, I think it is good to know who started the workflow, to see this into the logs and the details of the run too.

[agilgur5]

If they are submitting via the UI and CLI, there is an existing Workflow Creator feature that will add workflows.argoproj.io/creator labels based on available information.