caddyhttp: Add status_code option to http_redirect listener wrapper

[hsdfat]

Closes #6499

The http_redirect listener wrapper always answered plaintext HTTP requests on the HTTPS port with a 308. This adds a status_code option so the redirect can be made non-permanent (e.g. 307) or use another redirect code.

• JSON: "status_code": 307 (default remains 308); validated to be one of 301, 302, 303, 307, 308.
• Caddyfile (the wrapper previously had no Caddyfile options):

{
	servers {
		listener_wrappers {
			http_redirect {
				status_code 307
			}
			tls
		}
	}
}

Tests: unit tests that send a plaintext request through the wrapped listener and check the written status line and Location for each code, validation and Caddyfile parsing tables, and a caddyfile_adapt test.

Assistance Disclosure

I used AI assistants (Claude, OpenAI models) while writing and reviewing this change; I verified the behaviour and tests myself.

[CLAassistant]

All committers have signed the CLA.

[steadytao]

Looks decent. CLA needs to be signed.