Add priority queue support

[hylje]

Use the power of Redis Lua scripting to implement priority queueing by sorting the queue list for each job priority.

While this approach has its limits if the queue is very long, as each insert iterates the entire queue at most twice, it is fully compatible with existing queue consumers who don't need to know about job priorities.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 95.32164% with 8 lines in your changes missing coverage. Please review.

Project coverage is 91.79%. Comparing base (e4443b3) to head (3600318).

Files with missing lines	Patch %	Lines
minique/models/job.py	76.66%	6 Missing and 1 partial ⚠️
minique_tests/test_priority.py	98.79%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #38      +/-   ##
==========================================
+ Coverage   91.11%   91.79%   +0.68%     
==========================================
  Files          25       27       +2     
  Lines         855     1012     +157     
  Branches      115       93      -22     
==========================================
+ Hits          779      929     +150     
- Misses         45       51       +6     
- Partials       31       32       +1     

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