Add resultsActionBar and resultsFirstColumnCell slot registries to Explore and Discover plugins

[wanglam]

Description

This PR adds extensibility support to both the Explore and Discover plugins by introducing two new slot registries:

• resultsActionBar: Allows plugins to add custom action items to the results action bar
• resultsFirstColumnCell: Enables plugins to customize the first column cell rendering in data tables

These slots provide a standardized way for other plugins to extend the functionality of search results display without modifying core plugin code.

Screenshot

• For discover plugin

• For explore plugin

Testing the changes

Changelog

• feat: Add resultsActionBar and resultsFirstColumnCell slots to explore and discover plugin

Check List

• All tests pass
  • yarn test:jest
  • yarn test:jest_integration
• New functionality includes testing.
• New functionality has been documented.
• Update CHANGELOG.md
• Commits are signed per the DCO using --signoff

[codecov]

Codecov Report

❌ Patch coverage is 87.09677% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 60.51%. Comparing base (9001b68) to head (6325d04).

Files with missing lines	Patch %	Lines
...ublic/application/view_components/canvas/index.tsx	0.00%	3 Missing ⚠️
...on/components/default_discover_table/table_row.tsx	77.77%	0 Missing and 2 partials ⚠️
...mponents/results_action_bar/results_action_bar.tsx	0.00%	1 Missing ⚠️
src/plugins/discover/public/plugin.ts	50.00%	1 Missing ⚠️
...tion_bar/results_action_bar/results_action_bar.tsx	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #10773      +/-   ##
==========================================
+ Coverage   60.50%   60.51%   +0.01%     
==========================================
  Files        4485     4487       +2     
  Lines      120184   120244      +60     
  Branches    19911    19920       +9     
==========================================
+ Hits        72715    72768      +53     
- Misses      42426    42431       +5     
- Partials     5043     5045       +2     

Flag	Coverage Δ
Linux_1	26.57% <0.00%> (-0.02%)	⬇️
Linux_2	38.82% <ø> (ø)
Linux_3	39.08% <78.78%> (+0.01%)	⬆️
Linux_4	33.29% <45.16%> (+<0.01%)	⬆️
Windows_1	26.58% <0.00%> (-0.02%)	⬇️
Windows_2	38.79% <ø> (ø)
Windows_3	39.09% <78.78%> (+0.02%)	⬆️
Windows_4	33.29% <45.16%> (+<0.01%)	⬆️

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