feat: add response headers to HttpException

[karel-rehor]

Proposed Changes

• Add Headers to HttpException
• Make Headers easily accessible in WriteErrorEvent
• Add Example showing how to use these changes
• Add tests of these changes

Checklist

• CHANGELOG.md updated
• Rebased/mergeable
• A test has been added if appropriate
• dotnet test completes successfully
• Commit messages are conventional
• Sign CLA (if not already signed)

[alespour]

I do not have a strong opinion on this, but since Headers property in RestResponse class is nullable (T?), I think it should be here too, ie.

Suggested change

	public IEnumerable<HeaderParameter> Headers;
	public IEnumerable<HeaderParameter>? Headers { get; set; }

And, using a property is more common than a plain field, and follows the style of existing code.
Otherwise good to go after CHANGELOG is updated. The amount of test coverage of the new feature is outstanding.

[karel-rehor]

Added as suggested

[alespour]

LGTM now!

[bednar]

LGTM 🚀