Obsolete API warnings for ASP.NET Core need to be created in the aspnetcore.docs repo starting with .NET 10 and on.

Currently documentation on diagnostics warning for ASP.NET Core are located here, which also seems like a good location for adding the Obsolete API warnings:
:
https://github.com/dotnet/AspNetCore.Docs/tree/main/aspnetcore/diagnostics

The existing documentation on diagnostics warning for ASP.NET Core uses 3 prefixes, (although a bit cryptic):
They are: asp, bl and mvc
Examples:
https://github.com/dotnet/AspNetCore.Docs/blob/main/aspnetcore/diagnostics/asp0028.md
https://github.com/dotnet/AspNetCore.Docs/blob/main/aspnetcore/diagnostics/bl0001.md
https://github.com/dotnet/AspNetCore.Docs/blob/main/aspnetcore/diagnostics/mvc1000.md

I proposed we add one more here but use a more descriptive prefix like this:
asp-api-obsoleteXXXX.md where XXXX is the ID for the warning set in the product source.

The TOC lists these under Code Analysis, but we might consider changing that to Compiler Diagnostics instead to fit them all under one description that makes sense.

How to find the ASP.NET Core obsolete API for .NET 10 that need to be documented:

1. Search for the string "REMOVED" in all "*.unshipped.txt" files in the 10.0 branch.
   or
2. Search across the source code for use of ObsoleteAttribute to get a list of everything to document and either compare that to what has been documented so far (which has been up to .NET 9 on the donet docs repo) or cross check against when the attribute was added.

Example:
[Obsolete("IWebHost is obsolete. Use IHost instead. For more information, visit https://aka.ms/aspnet/deprecate/008.", DiagnosticId = "ASPDEPR008", UrlFormat = Obsoletions.AspNetCoreDeprecate008Url)]