docs: change message transformation 'enable' flag to no-doc

apps/emqx_message_transformation/src/emqx_message_transformation_schema.erl

@@ -63,7 +63,10 @@ fields(transformation) ->
     [
         {tags, emqx_schema:tags_schema()},
         {description, emqx_schema:description_schema()},
-        {enable, mk(boolean(), #{desc => ?DESC("config_enable"), default => true})},
+        {enable,
+            mk(boolean(), #{
+                desc => ?DESC("config_enable"), default => true, importance => ?IMPORTANCE_NO_DOC
+            })},
         {name,
             mk(
                 binary(),

rel/config/ee-examples/message-transformation.conf.example

@@ -0,0 +1,21 @@
+message_transformation {
+  transformations = [
+    {
+      name = trans1
+      description = ""
+      failure_action = ignore
+      log_failure {level = warning}
+      operations = [
+        {
+          key = topic
+          value = "concat([clientid,'/',topic])"
+        }
+      ]
+      payload_decoder {type = none}
+      payload_encoder {type = none}
+      topics = [
+        "#"
+      ]
+    }
+  ]
+}