Update Umberto to version 8.x to enable the new "Gloria" documentation theme #18875
Description
📝 Provide a description of requested docs changes
Our project is currently using Umberto 7.x, which is limited to the legacy "Umberto" documentation theme. Version 8.x introduces support for a new theme called "Gloria", which provides a more modern design, improved readability, and better UX.
Why:
- Gloria is the official successor to the old Umberto theme
- Improved compatibility with modern browsers and responsive layouts
- Aligns with future updates in the CKEditor ecosystem