Add build configuration parameter to enable `Debug` or `Release` builds

[philippzagar]

Add build configuration parameter to enable Debug or Release builds

:recycle: Current situation & Problem

As of now, there is no option to adjust the build configuration of the xcodebuild-or-fastlane.yml GitHub Action. This functionality would be very useful, especially for important production builds or repos that rely on low-layer Swift functionality.

:gear: Release Notes

• Add build configuration parameter to xcodebuild-or-fastlane.yml to enable Debug or Release builds

:books: Documentation

Proper documentation of parameter

:white_check_mark: Testing

Tested in the https://github.com/StanfordSpezi/.github repo which contains a very similar GitHub action.

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