MINOR: proto_htx: Add functions to check the cacheability of HTX messages

It is more or less the same than legacy versions but adapted to be called from
HTX analyzers. In the legacy versions of these functions, we switch on the HTX
code when applicable.
diff --git a/include/proto/proto_http.h b/include/proto/proto_http.h
index 0598df8..2961eae 100644
--- a/include/proto/proto_http.h
+++ b/include/proto/proto_http.h
@@ -73,6 +73,8 @@
 int htx_req_replace_stline(int action, const char *replace, int len,
 			   struct proxy *px, struct stream *s);
 void htx_res_set_status(unsigned int status, const char *reason, struct stream *s);
+void htx_check_request_for_cacheability(struct stream *s, struct channel *req);
+void htx_check_response_for_cacheability(struct stream *s, struct channel *res);
 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);