Moving solidus_sample to be development dependency

[softr8]

Summary

Solidus Sample gem includes seed data to setup local development in an easy way, it includes catalogs for countries, states, products, taxonomies/taxons and images. This gem itself needs about 10mb of disk space and most of the times it is only needed in local development or one time.

Example

~ $ du -a /app/vendor/bundle/ruby/2.7.0/gems/ 2>/dev/null | sort -n -r | head -n 100
363848	/app/vendor/bundle/ruby/2.7.0/gems/
...
9696	/app/vendor/bundle/ruby/2.7.0/gems/solidus_sample-2.11.15
9648	/app/vendor/bundle/ruby/2.7.0/gems/solidus_sample-2.11.15/db
9640	/app/vendor/bundle/ruby/2.7.0/gems/solidus_sample-2.11.15/db/samples

Checklist

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[elia]

This is a great idea!

Could you please move the dependency to the main Gemfile and also change the core install_generator so that it will add it to the host application Gemfile (with group: :development)?

[codecov]

Codecov Report

Attention: Patch coverage is 33.33333% with 2 lines in your changes missing coverage. Please review.

Project coverage is 88.65%. Comparing base (64f6a58) to head (6eb253e).
Report is 1139 commits behind head on main.

Files with missing lines	Patch %	Lines
...ib/generators/solidus/install/install_generator.rb	33.33%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5591      +/-   ##
==========================================
- Coverage   88.66%   88.65%   -0.02%     
==========================================
  Files         683      683              
  Lines       16293    16296       +3     
==========================================
+ Hits        14446    14447       +1     
- Misses       1847     1849       +2     

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[tvdeyen]

This is a really good idea. Do you mind to update the PR?