Support adding all plugins, including utilities, to Meltano through the hub

It would be awesome if like taps and targets you could submit utility plug-ins, (and other plug-ins), into Meltano through the hub.

For example: I've been working on a notebook utility that I use as a custom plug-in in Meltano. I think adding it to Meltano would benefit others, and it being on the hub and making it easy to find/read about would make it even better.