allow passing a custom ArqRedis class to create_pool

[jvllmr]

I would like to extend the functionality of the ArqRedis in one of my projects, but I also want to use the original create_pool function. It would be great if the create_pool function would accept a custom class which extends ArqRedis

[codecov-commenter]

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Codecov Report

Attention: Patch coverage is 40.00000% with 3 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
arq/connections.py	40.00%	3 Missing ⚠️

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@@ Coverage Diff @@ ## main #495 +/- ## ========================================== - Coverage 96.27% 96.10% -0.17%  ========================================== Files 11 11 Lines 1074 1079 +5 Branches 209 190 -19 ========================================== + Hits 1034 1037 +3  - Misses 19 21 +2  Partials 21 21 

Files with missing lines	Coverage Δ
arq/connections.py	87.50% <40.00%> (-2.57%)	⬇️

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