Ensure that when the container image is installing pymupdf (unavailable
in the repos) with verified hashes. To do so, it has the pymupdf
dependency declared in a "container" group in `pyproject.toml`, which
then gets exported into a requirements.txt, which is then used for
hash-verification when building the container.
Because this required modifying the container image build scripts, they
were all merged to avoid duplicate code. This was an overdue change
anyways.
