feat: set-up pre-commit hooks for automatic code formatting

[aleaf]

This commit sets up the framework for pre-commit hooks, which can run black and isort (and other tools) each time a commit is made, so that each commit is correctly formatted. More here, and in the contributing instructions.

[codecov]

Codecov Report

Merging #1713 (6399f47) into develop (2552de5) will increase coverage by 0.0%.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           develop   #1713   +/-   ##
=======================================
  Coverage     71.9%   71.9%           
=======================================
  Files          253     253           
  Lines        55891   55891           
=======================================
+ Hits         40202   40206    +4     
+ Misses       15689   15685    -4     

Impacted Files	Coverage Δ
flopy/utils/get_modflow.py	63.9% <0.0%> (+0.9%)	⬆️

[wpbonelli]

Auto-linting seems nice from a developer perspective and enforcing format locally could save CI cycles e.g. forgetting to run scripts/pull_request_prepare.py. Could be removed and pre-commit moved from optional to lint dep group if others agree

[langevin-usgs]

@aleaf, thanks for putting this together. It would be very nice to have a way to deal with this. I think everyone gets scolded by the CI linter on a regular basis. A concern, though, is how to keep version numbers up to date with what is running in Actions. For example, will we run into trouble when a new version of black is released?