fix: Returning .userCancelled when the app goes to the background during a Liveness check.

[ruisebas]

Issue #, if available:

• https://github.com/aws-amplify/amplify-ui-swift-liveness/issues/166

Description of changes: This PR maps the internal LivenessError.viewResignation error to the public FaceLivenessDetectionError.userCancelled, so that we report that one when the user sends the app to the background during a liveness check.

Check points: (check or cross out if not relevant)

• [ ] Added new tests to cover change, if needed
• [ ] Build succeeds with all target using Swift Package Manager
• [ ] All unit 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
• [ ] 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[bot]]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 30.44%. Comparing base (f13bf5e) to head (7dff2b4). Report is 3 commits behind head on main.

Files	Patch %	Lines
...ess/Views/Liveness/FaceLivenessDetectionView.swift	0.00%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #167 +/- ## ======================================= Coverage 30.44% 30.44% ======================================= Files 57 57 Lines 2230 2230 ======================================= Hits 679 679 Misses 1551 1551 ```

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