[v10.0.x] Timeseries: Graph series override stack migration (#68492)

Timeseries: Graph series override stack migration (#68491)

(cherry picked from commit e0d8f3b4a7)

Co-authored-by: Adela Almasan <88068998+adela-almasan@users.noreply.github.com>

public/app/plugins/panel/timeseries/migrations.ts

@@ -263,7 +263,7 @@ export function graphToTimeseriesOptions(angular: any): {
           case 'stack':
             rule.properties.push({
               id: 'custom.stacking',
-              value: { mode: StackingMode.Normal, group: v },
+              value: getStackingFromOverrides(v),
             });
             break;
           case 'color':
@@ -733,3 +733,11 @@ function getLegendHideFromOverride(reducer: ReducerID.allIsZero | ReducerID.allI
     ],
   };
 }
+
+function getStackingFromOverrides(value: Boolean | string) {
+  const defaultGroupName = defaultGraphConfig.stacking?.group;
+  return {
+    mode: value ? StackingMode.Normal : StackingMode.None,
+    group: isString(value) ? value : defaultGroupName,
+  };
+}