player allow/deny via addition of support for allowlist.json

[tadhunt]

For my limbo server use case, I need to allow only certain users to be able to join. I noticed the limbo server doesn't support this functionality, so I added it. Not sure if this is useful for the community, but I'm sharing it back in case it is.

• It processes allowlist.json files in the same format as standard Minecraft servers.
• If no allowlist.json exists, it allows the player to connect.
• If it fails to parse the allowlist, it doesn't allow the player to connect.
• If the player's UUID shows up in the allowlist, it allows the player to connect, otherwise it doesn't allow them.
• If the server.properties reduced-debug-info flag is set to false, then it sends a message to the console each time it allows or denies a user.

[LOOHP]

It's probably a better idea to load the list into memory and then check from there instead of reading the file every time a player joins. But that's a good feature to have :)

[tadhunt]

OK, I've fleshed out the implementation as recommended + added a default command to reload the allowlist. See the commit log for more details.

[tadhunt]

friendly ping

[LOOHP]

Sorry about the delay, I have not forgotten about this. I'll merge it when I have the time to also flesh out the changes! Thanks! (Most likely when 1.19.3 is released)