Aspnetcore.docs: Add more information on the new endpoint routing

[Rick-Anderson]

Need expanded coverage of endpointing routing changes to 3.0 - how they work, how they differ from 2.1 and previous routing.

currently have

An endpoint defines a delegate to process requests and a collection of arbitrary metadata. The metadata is used to implement cross-cutting concerns based on policies and configuration attached to each endpoint.
Add to that

For example, an Authorization Middleware can interrogate the endpoint's metadata collection for an [authorization policy](xref:security/authorization/policies#applying-policies-to-mvc-controllers).

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Document Details

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• ID: 32374077-e02e-d6a6-1cea-05e58447b7cd
• Version Independent ID: 86aeab13-1c25-9fc1-4e56-0390cb40c242
• Content: Routing in ASP.NET Core
• Content Source: aspnetcore/fundamentals/routing.md
• Product: aspnet-core
• Technology: aspnetcore-fundamentals
• GitHub Login: @Rick-Anderson
• Microsoft Alias: riande

[ShaneCourtrille]

Especially important as https://docs.microsoft.com/en-us/aspnet/core/migration/22-to-30?view=aspnetcore-3.0&tabs=visual-studio#routing-startup-code is pointing at this documentation for how to go from 2.2 to 3.0 :)

[Perustaja]

For someone who really only needs default routing, this was the most troublesome part of migrating my project from 2.2 to 3.0. It would be convenient if we had a more basic example starting from a default route and then adding in middleware/authorization for those out of the loop like myself.

[ghost]

Im not sure where the section ends> "Endpoint routing differences from earlier versions of routing"
From the standpoint of someone learning routing from scratch this section probably just confuses the subject. Do i skip this section?

[webczat]

well endpoint routing seems to be the new thing that should be used for all routing, but most examples are for 2.2 and earlier, mvc documentation still uses UsemVC etc etc. confusing