support ForwardedHeaders configuration

[WeihanLi]

Support ForwardedHeaders configuration

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Description

Support configure default forwarded Headers/KnownIPNetworks/KnownProxies from configuration

Fixes #57017

[WeihanLi]

@halter73 could you please spare some time on this? Looking forward to your input, thanks very much

[Copilot]

Pull Request Overview

This PR adds support for configuring ForwardedHeaders options through application configuration, allowing developers to specify custom forwarded headers, known networks, and known proxies via configuration rather than only through code.

• Extends ForwardedHeadersOptionsSetup to read additional configuration values for headers, networks, and proxies
• Adds parsing logic to handle comma-separated configuration values for forwarded headers and network/proxy collections
• Includes a new test to verify custom headers configuration works correctly

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 4 comments.

File	Description
src/DefaultBuilder/src/ForwardedHeadersOptionsSetup.cs	Adds configuration-based setup for forwarded headers, known networks, and known proxies with parsing logic
src/DefaultBuilder/test/Microsoft.AspNetCore.Tests/WebHostTests.cs	Adds test coverage for custom forwarded headers configuration