Add Classy ckeditor5-stylesheets config

As first step in order to test it as @bnjmnm propose is to create a simple patch to change into ckeditor5_stylesheets and then get ready for manual tests

I have modified the patch to add an additional key "ckeditor5-stylesheets" instead of replacing the "ckeditor_stylesheets" key to make the theme compatible ith both drupal/ckeditor (CKEditor 4) and drupal/ckeditor5

make a change to the patch to make it patch more reliable

No longer postponed as the blocking issue is now fixed.

Thanks @jrglasgow for the patch in #10. It applies applies smoothly.

#10 works for me with Classy 1.0.2 in D10.2.0. Setting to RTBC.

+1 RTBC

Doubt this will ever get fixed as classy is deprecated. But the patch works for us as well as we work into removing classy as our base theme.