fix(auth): use custom HTTPClient for HTTP Requests

[thisisabhash]

Issue #

In #3519, we upgraded aws-sdk-swift dependency to 0.36.1 and removed our custom http client engine to use aws-sdk-swift HTTP Client for making HTTP requests. This is causing latency increase in release/production builds for customers when making Auth category API calls(fetchAuthSession()/signIn()). This was released in 2.27.0.

Description

This PR reverts the change to use our custom HTTP Client which was used in 2.26.3 where the customer has confirmed that they are not experiencing the issue.

General Checklist

• Added new tests to cover change, if needed
• Build succeeds with all target using Swift Package Manager
• All unit tests pass
• All integration tests pass
• Security oriented best practices and standards are followed (e.g. using input sanitization, principle of least privilege, etc)
• Documentation update for the change if required
• PR title conforms to conventional commit style
• New or updated tests include Given When Then inline code documentation and are named accordingly testThing_condition_expectation()
• If breaking change, documentation/changelog update with migration instructions

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[thisisabhash]

Integration tests: https://github.com/aws-amplify/amplify-swift/actions/runs/8396784921

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 90 lines in your changes are missing coverage. Please review.

Project coverage is 68.20%. Comparing base (295521f) to head (cb2da44).
Report is 8 commits behind head on main.

Files	Patch %	Lines
...HttpClientEngine/FoundationClientEngineError.swift	0.00%	44 Missing ⚠️
...tpClientEngine/ClientRuntimeFoundationBridge.swift	0.00%	30 Missing ⚠️
...ustomHttpClientEngine/FoundationClientEngine.swift	0.00%	15 Missing ⚠️
...ls/CustomHttpClientEngine/PluginClientEngine.swift	0.00%	1 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3582      +/-   ##
==========================================
- Coverage   68.42%   68.20%   -0.23%     
==========================================
  Files        1077     1087      +10     
  Lines       36294    37043     +749     
==========================================
+ Hits        24835    25264     +429     
- Misses      11459    11779     +320     

Flag	Coverage Δ
API_plugin_unit_test	67.79% <ø> (+0.29%)	⬆️
AWSPluginsCore	66.27% <0.00%> (-0.63%)	⬇️
Amplify	48.21% <ø> (+0.11%)	⬆️
Analytics_plugin_unit_test	81.16% <ø> (ø)
Auth_plugin_unit_test	79.01% <ø> (-0.04%)	⬇️
CoreMLPredictions_plugin_unit_test	59.44% <ø> (ø)
DataStore_plugin_unit_test	81.33% <ø> (-1.04%)	⬇️
Geo_plugin_unit_test	70.75% <ø> (ø)
Logging_plugin_unit_test	62.87% <ø> (ø)
Predictions_plugin_unit_test	37.10% <ø> (ø)
PushNotifications_plugin_unit_test	87.13% <ø> (ø)
Storage_plugin_unit_test	77.65% <ø> (+0.03%)	⬆️
unit_tests	68.20% <0.00%> (-0.23%)	⬇️

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