Update TinyMCE editor to latest version

[rjkati]

Descriptive summary

The tinyMCE editor that is currently in use on the admin pages in Hyrax needs to be updated to the latest version (7, as of this writing). This update is needed to correct an accessibility issue documented in #6786 . It has been verified in #6786 that the issue is not present in version 7.

[rodyoukai]

Hi everyone,

I recently attempted to update the tinymce-rails gem to version 7 and tested several subversions within this release. Unfortunately, I encountered persistent issues during the asset precompilation process. Despite trying different approaches, the problem remains unresolved, and I believe it may be beyond my current capacity to fix.

Given these challenges, I would like to propose replacing tinymce-rails with the TinyMCE CDN. Using the CDN would bypass the asset precompilation entirely, streamlining the build process and potentially resolving the issues we're facing.

Dear @rjkati,
Would this be an acceptable solution for the project ? If you agree, I’d be happy to work on implementing this change.