json-schema-to-grammar : fix order of props + non-str const/enum (#6232)

* json: ordered json in server/schema converter to respect orig order

* json: ws nits

* json: support non-string const / enums

examples/server/server.cpp

@@ -30,7 +30,7 @@
 #include <signal.h>
 #include <memory>
 
-using json = nlohmann::json;
+using json = nlohmann::ordered_json;
 
 bool server_verbose = false;
 bool server_log_json = true;