Update disabled button color

[erinz2020]

1. update disabled buttons to a gray-ish color
2. add message under send to identification button on bulk import page about the reason why it's disabled

[codecov-commenter]

Codecov Report

❌ Patch coverage is 68.18182% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 8.59%. Comparing base (84c9a04) to head (4b59040).
⚠️ Report is 783 commits behind head on main.

Files with missing lines	Patch %	Lines
frontend/src/pages/BulkImport/BulkImportTask.jsx	0.00%	6 Missing ⚠️
frontend/src/components/BrutalismButton.jsx	88.88%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##              main   #1242      +/-   ##
==========================================
+ Coverage     8.57%   8.59%   +0.01%     
  Complexity     936     936              
==========================================
  Files          623     623              
  Lines        67974   67992      +18     
  Branches     12533   12493      -40     
==========================================
+ Hits          5832    5843      +11     
- Misses       61536   61548      +12     
+ Partials       606     601       -5     

Flag	Coverage Δ
backend	8.59% <68.18%> (+0.01%)	⬆️
frontend	8.59% <68.18%> (+0.01%)	⬆️

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[vkirkl]

Great! (Gray-t!)