Add fonts to Flatpak applications so that they are isolated from the system

[allahho31 at gmail.com]

Hi, I would like to thank you for your excellent effort at the level of
the idea of packing Flatpak ...
I want to add more fonts to Flatpak applications such as GIMP,
libreoffice,inkscape, ...etc. so that they are completely isolated from
the system, like Flatpak packages, I do not know how I can do that but
I wish to add that feature and important feature, I mainly use Flatpak
packages available on the flathub on the Fedora distribution