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

[ruisebas]

Issue #, if available:

• [iOS]Camera permission error occurs when entering the background #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]

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 ⚠️

Additional details and impacted files

@@           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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