Add yolov5 v6.0 pretrained model weights

[zhiqwang]

This is a follow-up PR of #194 and #196 .

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[codecov]

Codecov Report

Merging #206 (ca5c7f9) into main (ee108ad) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #206   +/-   ##
=======================================
  Coverage   96.98%   96.98%           
=======================================
  Files          10       10           
  Lines         630      631    +1     
=======================================
+ Hits          611      612    +1     
  Misses         19       19           

Flag	Coverage Δ
unittests	96.98% <100.00%> (+<0.01%)	⬆️

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Impacted Files	Coverage Δ
test/test_models.py	95.30% <100.00%> (+0.02%)	⬆️

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