separate custom namespace settings into two different fields

openpype/settings/defaults/project_settings/maya.json

@@ -1049,7 +1049,8 @@
             ]
         },
         "reference_loader": {
-            "naming": "{asset_name}_{subset}_:_GRP"
+            "namespace": "{asset_name}_{subset}",
+            "group_name": "GRP"
         }
     },
     "workfile_build": {

openpype/settings/entities/schemas/projects_schema/schemas/schema_maya_load.json

@@ -100,8 +100,13 @@
             "children": [
                 {
                     "type": "text",
-                    "label": "Naming",
-                    "key": "naming"
+                    "label": "Namespace",
+                    "key": "namespace"
+                },
+                {
+                    "type": "text",
+                    "label": "Group name",
+                    "key": "group_name"
                 },
                 {
                     "type": "label",