MINOR: http-ana/http-rules: Use dedicated function to forward internal responses

MINOR: http-ana/http-rules: Use dedicated function to forward internal responses

Call http_forward_proxy_resp() function when an internal response is
returned. It concerns redirect, auth and error reponses. But also 100-Continue
and 103-Early-Hints responses. For errors, there is a subtlety. if the forward
fails, an HTTP 500 error is generated if it is not already an internal
error. For now http_forward_proxy_resp() cannot fail. But it will be possible
when the new ruleset applied on all responses will be added.