Is that true for all plugins, or just this one?
All plugins should clone as the user discourse, otherwise if the plugin installs gems it can have permission issues.
I totally understand that, now that you say it, but none of the plugin install instructions I have ever seen say this. Take install a plugin, for example.
Is that true for docker_manager too?
Yes this is true of everything, we should follow one pattern, PR welcome to clean stuff up.