[Admin][UI] Allow select to include blank option

[chaimann]

[!NOTE] Split from #6228

Summary

Updates UI select component to allow including blank option. Drops support for passing options as html safe string, forcing choices to be an Array, and updates few places where options were still passed as strings.

Checklist

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[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 88.95%. Comparing base (ffa13fc) to head (9e32dad).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6279      +/-   ##
==========================================
- Coverage   88.95%   88.95%   -0.01%     
==========================================
  Files         860      860              
  Lines       18423    18419       -4     
==========================================
- Hits        16388    16384       -4     
  Misses       2035     2035              

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