Singularity / Apptainer support

[Lestropie]

While the process of generating the text files for minification is done using Docker, it should be possible for the minified container to be build using a Singularity definition file.

I wanted to move this to bookworm for consistency with the Docker container, but for some reason was having issues even at the apt stage, and the build process was taking a very long time making it hard to diagnose.