Replaced @popperjs/core with @floating-ui/dom.

As I am currently trying to work with Rails 8 and Importmaps I hit a wall due to PopperJS not being compatible, hence I migrated Flowbite to FloatingUI as asked for in #307. I hope I got everything right, since I am more familiar with Rails and plain JS, but I cross-checked the original docs with the generated ones (with `start:hugo`).