Nucleus does it, though I suggest that if you use Nucleus, you also pick up the Mixin plugin on the Nucleus releases page to improve it’s performance (though I’m hoping to PR my work into Sponge soon so that this is unnecessary, just need to find the time!). You can then use /nworld border gen.
An alternative is Project Borders (and I think Project Worlds does it as well, but I’m not sure), command for that is /border generate.