feat(storage): add support for upload presigned url

[harsh62]

Description

Extends the existing getUrl Storage API to support pre-signed URL generation for PUT (upload) operations, enabling developers to use third-party tools and HTTP clients to upload files to S3 via Amplify.

What changed

• New StorageAccessMethod enum at the category level (Amplify/Categories/Storage/StorageAccessMethod.swift) with .get and .put cases — follows the cross-platform naming convention from the approved mobile API review doc (Flutter, Android, Swift all use StorageAccessMethod)
• Updated AWSStorageGetURLOptions to accept a method: StorageAccessMethod parameter (defaults to .get)
• Updated AWSS3StorageGetURLTask to select AWSS3SigningOperation.putObject or .getObject based on the method parameter

Behavior

Option	Behavior
method: .get (default)	Existing behavior — generates a presigned download URL
method: .put	Generates a presigned URL for uploading via HTTP PUT
validateObjectExistence	Skipped when method is .put (object may not exist yet)
useAccelerateEndpoint	Works with both .get and .put
expiresIn	Works with both .get and .put

Usage

// Generate a presigned upload URL
let putURL = try await Amplify.Storage.getURL(
    path: .fromString("uploads/photo.jpg"),
    options: .init(
        pluginOptions: AWSStorageGetURLOptions(method: .put)
    )
)

// Use with any HTTP client
var request = URLRequest(url: putURL)
request.httpMethod = "PUT"
request.httpBody = fileData
let (_, response) = try await URLSession.shared.data(for: request)

Breaking Changes

None. The method parameter is optional and defaults to .get. Existing code continues to work unchanged.

Test Coverage

• Unit tests: Options initializer tests, task signing operation mapping, validation errors
• Property-based tests (100 iterations each): method-to-signing mapping, expiration forwarding, object existence validation conditional on method, accelerate forwarding
• Integration tests: Full round-trip PUT upload + GET download verification, existence validation skip for PUT, backward compatibility

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 66.79%. Comparing base (7c6a32a) to head (e5c8455).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4146      +/-   ##
==========================================
+ Coverage   66.53%   66.79%   +0.25%     
==========================================
  Files        1150     1150              
  Lines       43607    43617      +10     
==========================================
+ Hits        29013    29133     +120     
+ Misses      14594    14484     -110     

Flag	Coverage Δ
API_plugin_unit_test	68.42% <ø> (+0.20%)	⬆️
AWSPluginsCore	68.07% <ø> (ø)
Amplify	46.81% <ø> (ø)
Amplify_Foundation_Bridge_unit_test	62.28% <ø> (ø)
Amplify_Foundation_unit_test	67.64% <ø> (ø)
Analytics_plugin_unit_test	83.43% <ø> (ø)
Auth_plugin_unit_test	72.47% <ø> (+0.17%)	⬆️
DataStore_plugin_unit_test	82.77% <ø> (+0.90%)	⬆️
Firehose_plugin_unit_test	53.15% <ø> (ø)
Geo_plugin_unit_test	73.39% <ø> (ø)
Kinesis_plugin_unit_test	52.17% <ø> (ø)
Logging_plugin_unit_test	64.86% <ø> (ø)
Predictions_plugin_unit_test	33.89% <ø> (ø)
PushNotifications_plugin_unit_test	85.66% <ø> (ø)
RecordCache_unit_test	76.40% <ø> (ø)
Storage_plugin_unit_test	78.10% <100.00%> (+0.42%)	⬆️
unit_tests	66.79% <100.00%> (+0.25%)	⬆️

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