Update .NET AI Chat Web App template to support .NET 10

[danroth27]

Currently when I create a .NET AI Chat Web App template in VS it only offers me .NET 9 even if I have .NET 10 installed. We should update the template to support .NET 10.

@jeffhandley

[jeffhandley]

This is fixed with #7023. We will now offer net9.0 and net10.0, and net10.0 is the default. There was also an incompatibility with net10.0 for System.Linq.Async duplicate types fixed as part of this. Thanks for calling this out!