[FEAT]: Unhelpful hint when creating a user via invite link

[LeonKalt]

What would you like to see?

When sending an invite link and trying to register with an email you get Error: Could not create user. instead of a helpful hint. This leaves the user unsure on what to do. It should instead display, what is displayed in the logs

Username must only contain lowercase letters, periods, numbers, underscores, and hyphens with no spaces

[naaa760]

@LeonKalt please check!

[LeonKalt]

Great, this makes it a lot clearer :)