fix: set "fields" as a required config

apps/emqx_bridge_tablestore/src/emqx_bridge_tablestore.erl

@@ -294,11 +294,15 @@ fields_field() ->
     {fields,
         mk(
             hoconsc:array(ref(?MODULE, "tablestore_fields")), #{
-                default => [],
+                required => true,
+                validator => fun non_empty_list/1,
                 desc => ?DESC("desc_fields")
             }
         )}.
 
+non_empty_list([]) -> {error, empty_fields_not_allowed};
+non_empty_list(S) when is_list(S) -> ok.
+
 desc(Method) when Method =:= "get"; Method =:= "put"; Method =:= "post" ->
     ["Configuration for Tablestore using `", string:to_upper(Method), "` method."];
 desc("connector") ->