MEDIUM: proto_htx: Convert all HTTP error messages into HTX

During startup, after the configuration parsing, all HTTP error messages
(errorloc, errorfile or default messages) are converted into HTX messages and
stored in dedicated buffers. We use it to return errors in the HTX analyzers
instead of using ugly OOB blocks.
diff --git a/src/http.c b/src/http.c
index a556a88..bd8f96f 100644
--- a/src/http.c
+++ b/src/http.c
@@ -230,7 +230,7 @@
 	[HTTP_ERR_504] = 504,
 };
 
-static const char *http_err_msgs[HTTP_ERR_SIZE] = {
+const char *http_err_msgs[HTTP_ERR_SIZE] = {
 	[HTTP_ERR_200] =
 	"HTTP/1.0 200 OK\r\n"
 	"Cache-Control: no-cache\r\n"