specify supported python versions

[rkm]

We should document (and test) the supported python versions. As per https://devguide.python.org/versions/, 3.8 is the minimum supported, but only until 2024-10, so perhaps we should pick 3.9. Alternatively, the default version on Ubuntu 22.04 is 3.10, so that could be a sensible choice.

[howff]

I'd pick 3.10 for that reason but it has to run on smi04 etc which raises two questions

• how to get a newer python by default
• how a microservice or other caller can activate a virtualenv without having a wrapper shell script
  The answer to 2 would probably also solve 1

[rkm]

I've added 3.6 to the CI matrix now, alongside 3.10. We can remove 3.6 once we're off the old infrastructure.

I'm not sure I understand your second point, sorry! For non-interactive scripts, you don't need to activate the virtual env as you can just run venv/bin/python foo.py

[howff]

We can drop support for 3.6 now that the old infrastructure has gone.