Show how to configure properties of derived types

It would be a good idea to have examples showing the configuration of properties of derived types (like the `RssUrl` property having a max length or something.)

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#### Document Details

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* ID: e7106ae9-405f-8857-cd3e-571e966dea10
* Version Independent ID: 62ce23dc-9e20-525a-ea51-0dd76c1b7812
* Content: [Inheritance (Relational Database) - EF Core](https://docs.microsoft.com/en-us/ef/core/modeling/relational/inheritance)
* Content Source: [entity-framework/core/modeling/relational/inheritance.md](https://github.com/aspnet/EntityFramework.Docs/blob/master/entity-framework/core/modeling/relational/inheritance.md)
* Product: **entity-framework**
* GitHub Login: @rowanmiller
* Microsoft Alias: **divega**