Make JMusicBot error & shut down if ran in an unsupported manner

[MichailiK]

This PR adds a getUnsupportedBotReason utility, which determines if the bot JMusicBot is running under shows any remarks of being run in a manner that JMusicBot doesn't support. JDA will get shut down & JMusicBot will exit if there is a reason.

Right now, it only checks:

• If the bot is verified
• If the bot is public

It doesn't look like there's a way to check privileged intents with JDA 4? Thus its absent for now.

[MichailiK]

Whoops, the GUI prompt immediately disappears when JDA shuts down. Not exactly sure how to tackle that right now, so any suggestions would be welcome!

[tbodt]

I'm confused about why we have this, my bot is set to public and is working fine, at least as far as I can tell.

[sks316]

I'm confused as well. Until the latest update, my bot was set to public with absolutely no issues, then when I update, it stops working. I don't see the rationale behind this.
Fun fact, if the bot is set to auto start as a systemd service and meets one of these "unsupported" conditions, this new update causes it to hit the Discord API over 1,000 times in a short period, which makes Discord invalidate the bot token due to "potential abuse". That's the only way I knew anything was wrong, because I usually don't check the systemd logs after updating this.

[tbodt]

I just turned off update notifications - this one doesn't seem worth it.