Document IPNetwork and ForwardedHeadersOptions.KnownNetworks obsolescence for .NET 10

[Copilot]

This PR documents the breaking change introduced in .NET 10 Preview 7 where Microsoft.AspNetCore.HttpOverrides.IPNetwork and ForwardedHeadersOptions.KnownNetworks have been marked as obsolete in favor of System.Net.IPNetwork and ForwardedHeadersOptions.KnownIPNetworks.

The change affects developers using forwarded headers middleware who will now receive compiler warning ASPDEPR005 when using the obsolete APIs:

// Previous behavior - now obsolete
app.UseForwardedHeaders(new ForwardedHeadersOptions
{
    KnownNetworks.Add(new(IPAddress.Loopback, 8))
});

// New behavior - recommended approach
app.UseForwardedHeaders(new ForwardedHeadersOptions
{
    KnownIPNetworks.Add(new(IPAddress.Loopback, 8))
});

Changes made:

• Created new breaking change documentation at docs/core/compatibility/aspnet-core/10.0/ipnetwork-knownnetworks-obsolete.md
• Added ASP.NET Core section to the .NET 10 compatibility overview page
• Updated the table of contents to include the new ASP.NET Core 10.0 section

The documentation follows the established template and includes comprehensive migration guidance, affected APIs, and code examples to help developers update their applications.

Fixes #47622.

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Internal previews

📄 File	🔗 Preview link
docs/core/compatibility/10.0.md	Breaking changes in .NET 10
docs/core/compatibility/aspnet-core/10/ipnetwork-knownnetworks-obsolete.md	IPNetwork and ForwardedHeadersOptions.KnownNetworks are obsolete
docs/core/compatibility/toc.yml	docs/core/compatibility/toc