Add support for separate X/Z radius

[iLemon]

Suggestion: Add a way to specify a different max distance for the X and Z coordinate.

I have a world that is 43008×21504 in size. So the max distance from x: 0 z: 0 would be 21504 on x and 10752 on z.

[Phoenix616]

For now this is possible at least for a full world by setting the border with WorldBorder and just using the bigger radius as the plugin will not generate or teleport to coordinates outside the border.