Shop demo data

[denny]

Add some demo data for the Shop plugin.

Fix some long-standing issues with the demo data import/export tooling too, particularly around displaying the images on dev sites.

[codecov]

Codecov Report

❌ Patch coverage is 83.33333% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 99.98%. Comparing base (50607e1) to head (007c955).

Files with missing lines	Patch %	Lines
.../app/controllers/shiny_shop/products_controller.rb	80.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##              main    #2292      +/-   ##
===========================================
- Coverage   100.00%   99.98%   -0.02%     
===========================================
  Files          428      428              
  Lines         6167     6172       +5     
===========================================
+ Hits          6167     6171       +4     
- Misses           0        1       +1     

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