How to use argocd cli with multiple sources

[dormullor]

I would like to create an argocd app using the argocd app create command with multiple sources. there is a --ref flag but couldn't find any documentation on how to use it .
there is an example on creating argocd application with multi sources but with specifying the argocd yaml file, which doesn't help in my case.

This PR added the ability to add the --ref flag so maybe the feature owner can shed a light on that.

The main goal is to have the argocd app create as part of CICD process

@ishitasequeira