Adds the plugin list to the run command

[arcanis]

What's the problem this PR addresses?

I'm a new v2 user, and I'd like to use the shiny new workspaces foreach command. But when I run it, it tells me that the command is unknown. Since I'm a new user, I don't know anything about plugins and I just think that Yarn doesn't work.

Fixes #511

How did you fix it?

The plugins and their commands are stored within plugin-essentials. This allows us to suggest installing the right plugin when the user tries to execute a command that we don't ship by default.

This will only work for builtin scripts, of course.