Migrate YARP docs to AspNetCore.Docs repo

[Rick-Anderson]

Move https://github.com/dotnet/yarp/tree/main/docs/docfx/articles to the ASP.NET Core docs site,

TOC near this “Servers” section (maybe a peer called “YARP (Reverse Proxy)” or something?).

Contact is @adityamandaleeka & @samsp-msft

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Associated WorkItem - 372360

[samsp-msft]

I have added #34673 to split up some of the topics under Configuration as they included both config & extensibility content - splitting those docs into 2 will make them shorter and more relevant based on how the customer is using YARP.