[Manual][Backport 2.x] Improves connection pooling support for AWSSigV4 clients in data sources (#6135)

[bandinib-amzn]

Overview

This is cherry pick of 1999a23 from #6135

Testing

Testing with Node 14.

1. Create data source with Username and password authentication type.

2. Create data source with AWS SigV4 authentication type.

After creating data sources, following scenarios tested:

• Create index pattern
• Dev tool
• Discover
• Add sample data
• Visualizations
• Dashboards

[codecov]

Codecov Report

Attention: Patch coverage is 77.68595% with 27 lines in your changes are missing coverage. Please review.

Project coverage is 67.17%. Comparing base (98dfac8) to head (5edb124).
Report is 1 commits behind head on 2.x.

Files	Patch %	Lines
...data_source/server/legacy/http_aws_es/connector.js	64.40%	21 Missing ⚠️
...r/auth_registry/authentication_methods_registry.ts	33.33%	1 Missing and 1 partial ⚠️
...ins/data_source/server/util/credential_provider.ts	0.00%	2 Missing ⚠️
...gins/data_source/server/client/configure_client.ts	95.23%	0 Missing and 1 partial ⚠️
...ta_source/server/legacy/configure_legacy_client.ts	95.83%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##              2.x    #6176   +/-   ##
=======================================
  Coverage   67.17%   67.17%           
=======================================
  Files        3330     3331    +1     
  Lines       64313    64387   +74     
  Branches    10273    10281    +8     
=======================================
+ Hits        43204    43254   +50     
- Misses      18608    18636   +28     
+ Partials     2501     2497    -4     

Flag	Coverage Δ
Linux_1	35.07% <ø> (ø)
Linux_2	55.28% <ø> (ø)
Linux_3	44.71% <77.68%> (+0.10%)	⬆️
Linux_4	35.35% <ø> (ø)
Windows_1	35.10% <ø> (-0.04%)	⬇️
Windows_2	55.24% <ø> (ø)
Windows_3	44.71% <77.68%> (+0.08%)	⬆️
Windows_4	35.35% <ø> (ø)

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

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[bandinib-amzn]

Before rebase all CIs have been passed except WhiteSource Security check (which is expected).

[bandinib-amzn]

As per @AMoo-Miki, did testing for Node 14. Working as expected. Adding more details in PR Overview.

[ZilongX]

bootstrap somehow failed on ciGroup1, maybe wait for retry

[bandinib-amzn]

All checks are successful except WhiteSource Security checks (which is expected).