[Xamarin.Forms] `dotnet new xf-fsharp` should create a copy of net6.0-xamarinforms-fsharp

[TimLariviere]

Following this documentation: https://docs.microsoft.com/en-us/dotnet/core/tutorials/cli-templates-create-project-template

We need to package net6.0-xamarinforms-fsharp as a template compatible with dotnet new.
Ideally, we will be able to do: dotnet new xf-fsharp -n MyXFApp