apt.postgresql.org django app for www.postgresql.org

Hi,

We have implemented a repository browser for apt.postgresql.org to be
run on www.postgresql.org/repos/apt/. This has been in the works for
years, but has somehow never reached this list.

It is mostly feature-complete, i.e. browsing the list of supported
distributions, source and binary packages works. It supports searching
for packages and filenames in packages.

Dependencies:
python-apt, postgresql-*-debversion, pg_trgm (from postgresql-*-contrib)

To test, create a mirror of a (subset of) apt.postgresql.org:
* debmirror -v -h apt.postgresql.org -r pub/repos/apt --method=http -d sid-pgdg --omit-suite-symlinks -s main,12 -a source,amd64 --exclude='\.deb$' --getcontents --no-check-gpg /srv/repo
* set APT_DIR to that directory in settings_local.py
* run import-packagelists.py

TODO:
* The contained homepage at /repos/apt/ is an outdated mockup, the
list of supported dists should be rendered from the database
* There are no links to /repos/apt/ from anywhere else in the pg.o
page yet
* import-packagelists.py uses django to open the PG connection, but
this should be rewritten to use plain psycopg2.
* The idea is that import-packagelists.py writes directly to the
database, so appropriate GRANTs are needed to allow writing to the
apt_* tables only
* The "qa" part contains queries that have not yet been ported from an
older datamodel yet and is hence disabled
* There is no documentation yet

Still, it already works nicely if you point the browser directly at
/repos/apt, so please review :)

Christoph