feat: add support for versioning by version.py for python packages

[crwilcox]

No description provided.

[codecov]

Codecov Report

Merging #560 into master will decrease coverage by 0.08%.
The diff coverage is 74.54%.

@@            Coverage Diff             @@
##           master     #560      +/-   ##
==========================================
- Coverage   82.51%   82.42%   -0.09%     
==========================================
  Files          42       43       +1     
  Lines        4908     4963      +55     
  Branches      433      405      -28     
==========================================
+ Hits         4050     4091      +41     
- Misses        857      871      +14     
  Partials        1        1              

Impacted Files	Coverage Δ
src/releasers/python.ts	35.71% <6.66%> (-3.49%)	⬇️
src/updaters/python/version-py.ts	100.00% <100.00%> (ø)

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