chore(auth): update AppSyncSigner

[thisisabhash]

Issue #

None

Description

Update AWSCognitoAuthPlugin+AppSyncSigner signing logic to make it usable for both aws-appsync-events-swift and aws-appsync-apollo-extensions-swift repositories. The setting of host field in URLRequest headers before calling the SigV4 signing logic is now delegated to the individual repositories.

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

❌ Patch coverage is 0% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 68.04%. Comparing base (6e45ff1) to head (6c210e7).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...uthPlugin/AWSCognitoAuthPlugin+AppSyncSigner.swift	0.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4063   +/-   ##
=======================================
  Coverage   68.03%   68.04%           
=======================================
  Files        1129     1129           
  Lines       54486    54483    -3     
=======================================
+ Hits        37070    37071    +1     
+ Misses      17416    17412    -4     

Flag	Coverage Δ
API_plugin_unit_test	70.15% <ø> (ø)
AWSPluginsCore	69.50% <ø> (ø)
Amplify	47.87% <ø> (ø)
Analytics_plugin_unit_test	85.59% <ø> (ø)
Auth_plugin_unit_test	73.75% <0.00%> (-0.02%)	⬇️
DataStore_plugin_unit_test	83.60% <ø> (+0.06%)	⬆️
Geo_plugin_unit_test	75.95% <ø> (ø)
Logging_plugin_unit_test	65.56% <ø> (ø)
Predictions_plugin_unit_test	34.63% <ø> (ø)
PushNotifications_plugin_unit_test	88.76% <ø> (ø)
Storage_plugin_unit_test	78.90% <ø> (ø)
unit_tests	68.04% <0.00%> (+<0.01%)	⬆️

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