Change the tpye of ns from string to StringMsg

Signed-off-by: C88-YQ <1409947012@qq.com>

Author: C88-YQ

proto/gz/msgs/entity_factory_with_ns.proto

@@ -21,7 +21,7 @@ option java_package = "com.gz.msgs";
 option java_outer_classname = "EntityFactoryWithNsProtos";
 
 /// \ingroup gz.msgs
-/// \interface EntityFactory
+/// \interface EntityFactoryWithNs
 /// \brief Message with namespace to create new entities at a given pose.
 /// An entity can be created in one of the following ways:
 ///
@@ -34,6 +34,7 @@ import "gz/msgs/header.proto";
 import "gz/msgs/light.proto";
 import "gz/msgs/model.proto";
 import "gz/msgs/pose.proto";
+import "gz/msgs/stringmsg.proto";
 import "gz/msgs/spherical_coordinates.proto";
 
 message EntityFactoryWithNs
@@ -67,8 +68,8 @@ message EntityFactoryWithNs
   /// \brief New name for the entity, overrides the name on the SDF.
   string name                      = 8;
 
-  /// \brief New namespace for the entity, overrides the namespace on the SDF.
-  string ns                        = 9;
+  /// \brief Optional new namespace for the entity, overrides the namespace on the SDF.
+  StringMsg ns                        = 9;
 
   /// \brief Whether the server is allowed to rename the entity in case of
   /// overlap with existing entities.