[JDA] Message content intent

As of first September 2022, Discord **will** require bots to have a special (privileged) intent to read messages, if they are on more than 100 guilds.

Discord's devs have clearly stated, that this intent will not be granted to you if you want to use it for commands (!command something).

This makes the current JDA implementation pretty much unusable.

**Solutions**

There are two solutions I can think of:

1. Leave it like it is and essentially make it available only for private bots.
2. Redo the JDA implementation with complete slash command support.

In my opinion, the first solution would be unfortunate. However, I am not sure whether the second solution is even possible.

If you agree, I would do some research and if possible, choose the second solution.
This will break all backward compatibility for applications written for the current JDA implementation.

EDIT: The second option seems promising, I'm going to (attempt) to develop it in my fork. For now as another module. If anyone has any ideas what to add etc. please write them in this issue.