[Backport 2.x] [Multiple DataSource] Refactor test connection to support SigV4 auth type

[opensearch-trigger-bot]

Backport 02e0bc1 from #3456.

[codecov-commenter]

Codecov Report

Merging #3480 (7ebd972) into 2.x (1b1477c) will increase coverage by 0.01%.
The diff coverage is 53.57%.

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@@            Coverage Diff             @@
##              2.x    #3480      +/-   ##
==========================================
+ Coverage   66.43%   66.44%   +0.01%     
==========================================
  Files        3205     3205              
  Lines       61564    61567       +3     
  Branches     9494     9497       +3     
==========================================
+ Hits        40899    40911      +12     
+ Misses      18397    18384      -13     
- Partials     2268     2272       +4     

Flag	Coverage Δ
Linux	66.39% <53.57%> (+0.01%)	⬆️
Windows	66.40% <53.57%> (+0.02%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...components/create_form/create_data_source_form.tsx	75.00% <ø> (-0.27%)	⬇️
.../data_source_management/public/components/utils.ts	100.00% <ø> (+4.34%)	⬆️
...rce/components/edit_form/edit_data_source_form.tsx	67.85% <40.00%> (-2.89%)	⬇️
...gins/data_source/server/client/configure_client.ts	71.42% <66.66%> (+24.76%)	⬆️
...ata_source/server/client/configure_client_utils.ts	86.11% <66.66%> (+21.40%)	⬆️
.../plugins/data_source/server/data_source_service.ts	75.00% <100.00%> (+3.57%)	⬆️
...s/osd-optimizer/src/node/node_auto_tranpilation.ts	83.67% <0.00%> (-4.09%)	⬇️
packages/osd-optimizer/src/node/cache.ts	51.31% <0.00%> (-2.64%)	⬇️

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[kavilla]

@zhongnansu for future reference: #3456 (comment)