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

1. Copy Code from [EF-RP 6.0 project](https://github.com/dotnet/AspNetCore.Docs/tree/main/aspnetcore/data/ef-rp/intro/samples/cu60) to [cu90](https://github.com/dotnet/AspNetCore.Docs/tree/main/aspnetcore/data/ef-rp/intro/samples/cu90) and update for .NET 9

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](https://docs.microsoft.com/en-us/aspnet/core/data/ef-mvc/inheritance).
4. Consider adding code supporting [Tutorial: Learn about advanced scenarios - ASP.NET MVC with EF Core](https://docs.microsoft.com/en-us/aspnet/core/data/ef-mvc/advanced?view=aspnetcore-6.0).

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](https://docs.microsoft.com/en-us/aspnet/core/data/ef-mvc/intro?view=aspnetcore-6.0)~
and make a Blazor version.

@guardrex - @tdykstra

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#### Document Details

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* ID: 7a54c97f-ddd4-b041-5e5f-a2df009ace50
* Version Independent ID: fa488196-1f98-08ea-adcc-17d9dac86727 and 3e28328b-9c7a-359b-2f57-319b0bc7eea3
* Content: [Razor Pages with Entity Framework Core in ASP.NET Core - Tutorial 1 of 8](https://docs.microsoft.com/en-us/aspnet/core/data/ef-rp/intro) and https://learn.microsoft.com/en-us/aspnet/core/tutorials/razor-pages/?view=aspnetcore-8.0
* Content Source: [aspnetcore/data/ef-rp/intro.md](https://github.com/dotnet/AspNetCore.Docs/blob/main/aspnetcore/data/ef-rp/intro.md) and https://github.com/dotnet/AspNetCore.Docs/blob/main/aspnetcore/tutorials/razor-pages/index.md
* Product: **aspnet-core**
* Technology: **aspnetcore-data**
* GitHub Login: @Rick-Anderson
* Microsoft Alias: **riande**

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[Associated WorkItem - 33228](https://dev.azure.com/msft-skilling/Content/_workitems/edit/33228)