Make it possible to edit String Purpose for iOS apps

Context

When deploying TotalCross apple applications for apple store, the review returns warnings about missing String purpose required when you use sensible features in terms of privacy such as location and camera. In order to solve this, we need to make it possible to edit String purpose on the package process, by providing api for such a configuration.

Devices:

• Device: apple devices
• iOS

Additional context

bellow the warning returned by the review:

ITMS-90683: Missing Purpose String in Info.plist - Your app's code references one or more APIs that access sensitive user data. The app's Info.plist file should contain a NSLocationAlwaysUsageDescription key with a user-facing purpose string explaining clearly and completely why your app needs the data. Starting Spring 2019, all apps submitted to the App Store that access user data are required to include a purpose string. If you're using external libraries or SDKs, they may reference APIs that require a purpose string. While your app might not use these APIs, a purpose string is still required. You can contact the developer of the library or SDK and request they release a version of their code that doesn't contain the APIs. Learn more (https://developer.apple.com/documentation/uikit/core_app/protecting_the_user_s_privacy).