Add pre-commit as optional developer tool

[dbluhm]

This PR adds pre-commit and associated configuration. This is more or less a tool for installing git hooks that check flake8 and black before committing. When used, this helps prevent follow up commits for formatting changes with black or correcting complaints from flake8.

There is also a configuration for installing hooks for checking that the commit message conforms to conventional commits.

It is possible to use the pre-commit hooks (flake8 and black) without the commit-msg hooks (commitlint) and vice-versa. Contributors can also ignore pre-commit altogether -- this is purely opt-in and must be explicitly installed.

Pre-commit is a pretty widely used tool in the python community and is analogous to husky in the javascript community. I've had these configuration files hanging out in my local fork of the ACA-Py repo and have been happily using them for more than a year.

[codecov-commenter]

Codecov Report

Merging #1671 (3812a8e) into main (3774e85) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #1671   +/-   ##
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  Coverage   95.50%   95.50%           
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  Files         528      528           
  Lines       32766    32766           
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  Hits        31293    31293           
  Misses       1473     1473