Support per-visualization entityName override

Remove entityName from the required fields of dashboard-group-descriptor so group definitions no longer must specify an entity. Add an optional entityName string property to dashboard-visualization-descriptor (minLength: 1) so individual visualizations can override the group's entityName. If the visualization-level entityName is omitted, the group's entityName is used.

lowcode/schema/definitions/dashboard-group-descriptor.schema.json

@@ -49,6 +49,6 @@
       "minItems": 1
     }
   },
-  "required": ["name", "entityName", "visualizations"],
+  "required": ["name", "visualizations"],
   "additionalProperties": false
 }

lowcode/schema/definitions/dashboard-visualization-descriptor.schema.json

@@ -36,6 +36,11 @@
       "description": "Allow users to click to see underlying records",
       "default": false
     },
+    "entityName": {
+      "type": "string",
+      "description": "Override entity for this visualization. If omitted, uses the group's entityName.",
+      "minLength": 1
+    },
     "number": {
       "$ref": "dashboard-number-descriptor.schema.json"
     },