Docker login for private registries with swarm

[rstefanic]

After looking through the other issues in this repo, I've noticed that other people who are doing a deployment in swarm mode have passed --with-registry-auth in args for their docker swarm command. But I'm wondering how people with examples like this have logged into their private registries using this action. I've tried running docker/login-action before running this action to see if that would work like another Docker Swarm deployment action, but that's not working for me.

Is there a way that people are running docker login to log into a private registry before running the action to deploy to a swarm cluster? If there isn't I'd be more than happy to add that feature in here (something like expanding pre_deployment_command_args to work with swarm).