EPUB font download activation

[therealmarv]

Do NOT merge it into production because of problems with REX currently (2023-12-15)

Activate EPUB font download again (draft) by reverting the removal. Example see EPUB generation for third parties with font enabled https://github.com/openstax/ce/issues/2132

IMPORTANT:
This branch is a moment in time (2023-12-15). You have to update/merge Enki AND ce-styles current versions.

For Enki, it's simple

git fetch
git checkout epub-font-download-activate
git merge main
# maybe also commit & push the updates to github :)

For ce-styles within enki a little bit more complicated:

• Check which ce-styles is currently in usage in Enki main (probably the last tagged version)
• Merge that version into ce-styles

cd ce-styles
git checkout epub-font-download-activate
git fetch
git merge v1.xxx.0
# maybe also commit & push the updates to github :)