[Admin] Product form improvements

[chaimann]

Summary

A bit of cleanup for product form:

• add missing column gap between sections inside a panel
• add translations instead of raw strings
• update products controller to explicitly permit a list of params and fix saving multiple related ids by removing #split_params

Checklist

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 86.63%. Comparing base (2aed8c3) to head (b4b15bb).
Report is 12 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6270      +/-   ##
==========================================
- Coverage   88.86%   86.63%   -2.24%     
==========================================
  Files         857      520     -337     
  Lines       18415    11946    -6469     
==========================================
- Hits        16365    10349    -6016     
+ Misses       2050     1597     -453     

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[tvdeyen]

Thanks