.NET 8: Code only EF with RP add inheritance and advanced topics

[Rick-Anderson]

Update the code for Razor Pages with Entity Framework Core in ASP.NET Core - Tutorial 1 of 8 to .NET 8 or 9

1. Copy Code from EF-RP 6.0 project to cu80 and update for .NET 9 or .NET 8

2. Quick review of code and update where necessary.

3. Add code for inheritance. Hopefully you can use some of the code from Tutorial: Implement inheritance - ASP.NET MVC with EF Core.

4. Consider adding code supporting Tutorial: Learn about advanced scenarios - ASP.NET MVC with EF Core.

Once the preceding is complete, we'll port all the RP code and update the Tutorial: Get started with EF Core in an ASP.NET MVC web app

Also tracked in dotnet/AspNetCore.Docs#26505