Update target version to 12.0

[MikhailSuendukov]

• [x] Has CHANGELOG.md been updated?
• [x] Are the files formatted correctly?
• [x] Did you test your change with either the sample apps that are included in the repository or with a blank app that uses your change?

Description

During the build process, warnings indicate that AppCenter targets iOS 11, even though the minimum supported version is iOS 12. So we raised target versions for iOS and tvOS to 12.0.

Related PRs or issues

AB#107365