fix(Auth): Adding credentialsProvider to Cognito clients

[harsh62]

Issue #

#3743

Description

When initializing the Cognito client, there was no credentialsProvider initialized. This change introduce the initialization of the credentialsProvider from the AuthService.

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.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 68.44%. Comparing base (53d0fff) to head (86b68b7).
Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3745   +/-   ##
=======================================
  Coverage   68.43%   68.44%           
=======================================
  Files        1079     1079           
  Lines       37569    37573    +4     
=======================================
+ Hits        25711    25715    +4     
  Misses      11858    11858           

Flag	Coverage Δ
API_plugin_unit_test	68.83% <ø> (-0.04%)	⬇️
AWSPluginsCore	68.56% <ø> (ø)
Amplify	47.65% <ø> (+0.06%)	⬆️
Analytics_plugin_unit_test	84.52% <ø> (ø)
Auth_plugin_unit_test	79.44% <100.00%> (+0.01%)	⬆️
DataStore_plugin_unit_test	81.17% <ø> (-0.06%)	⬇️
Geo_plugin_unit_test	72.00% <ø> (ø)
Logging_plugin_unit_test	62.95% <ø> (ø)
Predictions_plugin_unit_test	37.32% <ø> (ø)
PushNotifications_plugin_unit_test	86.21% <ø> (ø)
Storage_plugin_unit_test	76.75% <ø> (ø)
unit_tests	68.44% <100.00%> (+<0.01%)	⬆️

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