Add support for authenticated registries

[ehelms]

Enables foremanctl to authenticate with private registries by checking for auth files before attempting image pulls. Users can run podman login <registry> --authfile=/etc/foreman/registry-auth.json and foremanctl will automatically use the credentials when available.

[pablomh]

This has worked fine with #369, so I guess that my recommendation could be ammended if needed later.

[pablomh]

Thinking about this, how would it fit with future rootless containers which probably won't have access to the auth file?

[ehelms]

Thinking about this, how would it fit with future rootless containers which probably won't have access to the auth file?

In that case, the authentication file would be located in a different location I think. Relative to the user's home for example. I am hesitant to optimize for that.

[evgeni]

tasks already runs after roles, so why using post_tasks here?

[ehelms]

Cause that ordering is not obvious, while I find post_tasks to be self-documenting in terms of order.

[evgeni]

does it work if we set it to None here?

Suggested change

	redis_registry_auth_file: /etc/foreman/registry-auth.json
	redis_registry_auth_file:

As we should try to keep the role free of Foreman specifics

[ehelms]

I suppose. This is foremanctl so it's kinda in the name? 😁