feat: [v1] Updating minimum deployment target to iOS 12

[ruisebas]

Description

This PR bumps the deployment target to iOS 12 in preparation for some upcoming changes.

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
  • https://github.com/aws-amplify/amplify-swift/actions/runs/8102435761 Old
  • https://github.com/aws-amplify/amplify-swift/actions/runs/8853341462
• 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.