Supporting .NET 8.0

Starting from MR 3391, the PowerServer Web API solution supports .NET 8.0.

After applying MR 3391, the user can choose the target framework as .NET 6.0 or .NET 8.0 when generating the PowerServer Web API solution.

But notice that SnapDevelop does not support .NET 8.0 (it supports only .NET 6.0). If the user wants to edit a ".NET 8" PowerServer Web API solution (such as configuring the auth template), due to the fact that SnapDevelop does not support .NET 8, the user has to use an external C# IDE that supports .NET 8, such as Visual Studio.