Make middleware fully configurable

[sondrelg]

This is mostly a reimplementation of #15, motivated by #38. It will require us to bump a major version, since we are removing some backwards compatibility, but I think it's for the best.

In short, the PR replaces the built-in uuid4 generation and validation with concepts of:

• a generator function to create new ID values when needed
• a validator function to optionally validate incoming header values (and discard failed ones), and
• a transformer function to optionally clean header values

[codecov[bot]]

Codecov Report

Merging #39 (24b5530) into main (0c6fd1e) will not change coverage. The diff coverage is 100.00%.

@@            Coverage Diff            @@
##              main       #39   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           11        11           
  Lines          314       353   +39     
=========================================
+ Hits           314       353   +39     

Impacted Files	Coverage Δ
asgi_correlation_id/middleware.py	100.00% <100.00%> (ø)
tests/conftest.py	100.00% <100.00%> (ø)
tests/test_extension_celery.py	100.00% <100.00%> (ø)
tests/test_middleware.py	100.00% <100.00%> (ø)

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[JonasKs]

Love this! I’ll do a review tomorrow👏

[sondrelg]

Think this addresses your comments @commentator8. If you have time and want to take another look, feel free 🙏

[commentator8]

@sondrelg You covered all my points and it looks good. The extra defensive if on the transformer was a nice touch :)