Added duduping on mb_trackid to the duplicates plugin

[tommyschnabel]

Description

plugins/duplicates: dedupe_mb_trackid_on_import option added to deduplicate during imports based on already-imported mb_trackid.

To Do

• Documentation. (If you've added a new command-line flag, for example, find the appropriate page under docs/ to describe it.)
• Changelog. (Add an entry to docs/changelog.rst to the bottom of one of the lists near the top of the document.)
• Tests. (Very much encouraged but not strictly required.)

[codecov]

Codecov Report

❌ Patch coverage is 20.83333% with 19 lines in your changes missing coverage. Please review.
✅ Project coverage is 68.72%. Comparing base (4572a7d) to head (f8be4bb).
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
beetsplug/duplicates.py	20.83%	19 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6313      +/-   ##
==========================================
- Coverage   68.78%   68.72%   -0.07%     
==========================================
  Files         140      140              
  Lines       18619    18642      +23     
  Branches     3054     3060       +6     
==========================================
+ Hits        12807    12811       +4     
- Misses       5164     5183      +19     
  Partials      648      648              

Files with missing lines	Coverage Δ
beetsplug/duplicates.py	19.68% <20.83%> (-0.32%)	⬇️

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