[WIP] Next Demo version

[tabacitu]

The next branch is where we bring together all fixes&features for our next version. This PR is here to document all PRs merged, all breaking changes, all remaining TODOs about this version until launch.

Changes

This PR uses:

• backpack/crud:dev-next - https://github.com/Laravel-Backpack/CRUD/pull/5715
• backpack/pro:dev-next - https://github.com/Laravel-Backpack/PRO/pull/297
• backpack/medialibrary-uploaders:dev-next - https://github.com/Laravel-Backpack/medialibrary-uploaders/pull/38

Breaking changes

[none, at the moment]

Todos

Things to do before we merge this PR into main:

• [x] put this online at https://next.backpackforlaravel.com
• [x] adjust composer.json to use the launched version