Preparation for Python 3.11 support (SYN-5095)

[vEpiphyte]

• Update library versions for lmdb, msgpack, tornado and xxhash
• Add python 3.11 to our CI tests as a optional job
• Update developer guide to note the cpython version in docker containers may change

[codecov]

Codecov Report

Patch coverage has no change and project coverage change: -0.11 ⚠️

Comparison is base (462c50e) 97.26% compared to head (3ece2f0) 97.16%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3070      +/-   ##
==========================================
- Coverage   97.26%   97.16%   -0.11%     
==========================================
  Files         222      222              
  Lines       43910    43909       -1     
==========================================
- Hits        42711    42665      -46     
- Misses       1199     1244      +45     

Flag	Coverage Δ
linux	97.16% <ø> (-0.01%)	⬇️
linux_replay	?

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
synapse/telepath.py	93.66% <ø> (-0.01%)	⬇️

... and 9 files with indirect coverage changes

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