The psycopg2-binary packages are not available from PyPI with 3.13
wheels and the docs[1] recommend that one install the package from
source when possible. The psycopg2-binary package will fall back to
source builds, we just need to ensure that the required apt dependencies
are installed.

[1] https://www.psycopg.org/docs/install.html#psycopg-vs-psycopg-binary

The CLI interface to apt is not stable and so we need to use apt-get
instead.

Re-work all uses of envsubst into equivalent build arg-based solutions
and remove envsubst all together. This had the knock-on effect of a)
moving additional Python requirements specification out of files and
into the dynamic pipeline config and b) allowed us to unify the
installed dependencies between the Debian and alpine-based Python
images.