Support having plugins as dependencies in shareable config

Problem

My shareable config uses rules from an external plugin and I would like to make it a `dependency` so the user doesn't have to manually install the plugin manually. I couldn't find any docs on this, but it doesn't seem to work, so I'll assume it's not currently supported. [code block] I assume it's because you only try to load the plugin when the config is finished merging. Other shareable configs that depend on a plugin instructs the users to manually install the plugin too and they have it in `peerDependencies`. I find this sub-optimal though and I don't want the users to have to care what plugins my config uses internally. The whole point of shareable configs is to minimize boilerplate and overhead, so this would be a welcome improvement. <bountysource-plugin> Want to back this issue? Post a bounty on it! We accept bounties via Bountysource. </bountysource-plugin>