add alternative parametrization for AssymetricLaplace

[aloctavodia]

What is this PR about?

This adds an alternative parametrization to AsymmetricLaplace distribution. This is parametrization is useful for quantile regression with the new parameter q being fixed at the quantile of interest.

Checklist

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• Are the changes covered by tests and docstrings?
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Major / Breaking Changes

• ...

Bugfixes / New features

• Add alternative parametrization to AsymmetricLaplace distribution. This parametrization is useful for quantile regression with the new parameter q being fixed at the quantile of interest.

Docs / Maintenance

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[codecov]

Codecov Report

Merging #6337 (6653917) into main (1a143b7) will increase coverage by 3.80%.
The diff coverage is 89.47%.

❗ Current head 6653917 differs from pull request most recent head 98f898c. Consider uploading reports for the commit 98f898c to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6337      +/-   ##
==========================================
+ Coverage   90.44%   94.25%   +3.80%     
==========================================
  Files         111      111              
  Lines       23985    24004      +19     
==========================================
+ Hits        21693    22624     +931     
+ Misses       2292     1380     -912     

Impacted Files	Coverage Δ
pymc/distributions/continuous.py	97.67% <84.61%> (-0.18%)	⬇️
pymc/tests/distributions/test_continuous.py	99.76% <100.00%> (+<0.01%)	⬆️
pymc/tests/gp/test_gp.py	100.00% <0.00%> (ø)
pymc/distributions/shape_utils.py	97.87% <0.00%> (+0.42%)	⬆️
pymc/distributions/logprob.py	67.28% <0.00%> (+5.55%)	⬆️
pymc/step_methods/hmc/quadpotential.py	80.62% <0.00%> (+6.77%)	⬆️
pymc/model_graph.py	78.82% <0.00%> (+12.35%)	⬆️
pymc/distributions/timeseries.py	94.45% <0.00%> (+65.99%)	⬆️
pymc/tests/step_methods/hmc/test_quadpotential.py	95.81% <0.00%> (+95.81%)	⬆️
pymc/tests/distributions/test_timeseries.py	99.51% <0.00%> (+99.51%)	⬆️

[ricardoV94]

Can you add a test? There are some tests for alternative parametrizations of other distributions that may be an easy template.