Request: disable Nostrum startup

[ProducerMatt]

I'm writing a chatbot app that supports multiple services simultaneously. So one deploy might be connected to Discord, Slack, and IRC, while another might just be IRC.

I wanted to disable Nostrum when there was no configuration for Discord. However it looks when Nostrum is in your dependencies, it is always started, unless you go jump through the hoops outlined in the multi-node setup.

I'd rather set a config flag or pass an atom to Nostrum in order to make it shut itself down.

[jchristgit]

You need to add nostrum to included_applications and add runtime: false to it in your mix.exs, as ni the multi-node doc. These options have no place in nostrum's configuration because they concern the way core OTP tooling deals with starting nostrum.