TODO: add AppImages with bundled FFmpeg builds

[bastimeyer]

With the upcoming removal of the i686 AppImages due to the EOL being reached by the manylinux2014 images today/tomorrow, this will allow bundling x86_64 and aarch64 FFmpeg builds into the new manylinux_2_28-based AppImages. Since this is only beneficial on some systems, this should be done optionally in secondary AppImage builds.

• https://github.com/pypa/manylinux/blob/095daf5fc97b98aa0f1e48c3a594df654caa09ee/README.rst#manylinux2014-centos-7-based-glibc-217
• https://peps.python.org/pep-0599/#rationale
• https://endoflife.date/centos