Add a ui/thumbnail component

[elia]

Summary

Checklist

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[codecov]

Codecov Report

Merging #5431 (4ceef99) into main (afc630e) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main    #5431   +/-   ##
=======================================
  Coverage   88.85%   88.86%           
=======================================
  Files         609      610    +1     
  Lines       14784    14791    +7     
=======================================
+ Hits        13137    13144    +7     
  Misses       1647     1647           

Files	Coverage Δ
...mponents/solidus_admin/products/index/component.rb	86.84% <ø> (ø)
...components/solidus_admin/ui/thumbnail/component.rb	100.00% <100.00%> (ø)

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[rainerdema]

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