Add a customizable motd while maintenance

[Yu-Dino]

No description provided.

[Pascalpex]

Hello @Yu-Dino and thank you for your first PR,

I like the idea to be able to change the MOTD when the server is in maintenance mode, however there are some things that need to be changed:

• You added a listener class ServerPingListener to send the MOTD. DeepslateMC however does not use bukkit event per convention and places bare code or method calls directly at the place where the events are created. I was also wondering why you put the listener inside the commands folder
• You added two new configuration options for the maintenance motd and the normal motd. It would be better to use only send a custom motd when the maintenance mode is active so that the default motd is used otherwise. Also make sure to use a String list instead of a String containing \n characters (See the tablist options for example).
• Its good that you added the ability to use minimessage or legacy format support but make sure to use a english default value instead of a german one for the motd.
• There should be an option to not change the motd when activating maintenance mode. You can either do this by adding a default value default or add a config option useCustomMotd or something like that

Finally make sure to test your changes because in the current state is does not work because you did not register the listener anywhere.

If you have any further questions, feel free to ask