Generate Xamarin client application

[Zenrac]

Overview of the feature request

• As we already have the possibility to get a Blazor front, and a ASP.core back, it could be interesting to have a way to generate a mobile application with .NET.
• Xamarin would allow to generate a cross platform application for both iOS and Android phones.
• Thanks to Xamarin we are able to share some code.

Work done before templating : https://github.com/nicolas63/JhipsterXamarin

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[Zenrac]

Fixed by #489