Add support for Python 3.11

[JPBergsma]

Python has released their second release candidate of python 3.11 and according to the original release schedule the first version of python 3.11 will be released next week.
It promises that it is on average 25% faster than previous releases of python, so I think we should start to work on adding support for python 3.11 to the optimade python tools.

[ml-evs]

Sounds good! Do you want to make a PR enabling as a Python version 3.11.0-rc.2 in our CI test matrix? It will probably fail for a very long time due to missing dependencies but we can at least use it for tracking.

[JPBergsma]

I still have several other things I would like to do first:

• Finish PR Aliases now also work for nested fields; Only retrieve data required for constructing a response from the database. #1304
• Add the Files endpoint issue Support for the /files endpoint #1225
• Update the code for the Bioxl database
• Make a new release
• Move away from the heroku server

So it may be a while before I get around to doing it.
Several dependencies like elasticsearch, fastapi and pyyaml are indeed not yet supporting python 3.11, so it may still take a while before we can add support for python 3.11. So I do not think it is urgent.
I guess I just got a little too excited that it would have a substantial performance improvement and would be released soon.
Feel free to work on this if you want.

[ml-evs]

Sure, I'll just make a quick PR that we can keep an eye on

[ml-evs]

The final blocker for Python 3.11 is aiida-core, which has fixed its requirement pins for py311 but has not yet made a release.