MINOR: proto_htx: Add functions htx_perform_server_redirect

It is more or less the same than legacy version but adapted to be called from
HTX analyzers. In the legacy version of this function, we switch on the HTX code
when applicable.
diff --git a/include/proto/proto_http.h b/include/proto/proto_http.h
index 40e82b2..0d3d7df 100644
--- a/include/proto/proto_http.h
+++ b/include/proto/proto_http.h
@@ -75,6 +75,7 @@
 void htx_check_request_for_cacheability(struct stream *s, struct channel *req);
 void htx_check_response_for_cacheability(struct stream *s, struct channel *res);
 int htx_send_name_header(struct stream *s, struct proxy *be, const char *srv_name);
+void htx_perform_server_redirect(struct stream *s, struct stream_interface *si);
 void htx_server_error(struct stream *s, struct stream_interface *si, int err, int finst, const struct buffer *msg);
 void htx_reply_and_close(struct stream *s, short status, struct buffer *msg);