Datasource: Fix - apply default query also to queries in new panels (#59625)

* apply default query also to new panels

* add comment

* add tests

public/app/core/utils/query.ts

@@ -9,6 +9,23 @@ export const getNextRefIdChar = (queries: DataQuery[]): string => {
   }
 };
 
+// This function checks if the query has defined properties beyond those defined in the DataQuery interface.
+export function queryIsEmpty(query: DataQuery): boolean {
+  const dataQueryProps = ['refId', 'hide', 'key', 'queryType', 'datasource'];
+
+  for (const key in query) {
+    // label is not a DataQuery prop, but it's defined in the query when called from the QueryRunner.
+    if (key === 'label') {
+      continue;
+    }
+    if (!dataQueryProps.includes(key)) {
+      return false;
+    }
+  }
+
+  return true;
+}
+
 export function addQuery(queries: DataQuery[], query?: Partial<DataQuery>, datasource?: DataSourceRef): DataQuery[] {
   const q = query || {};
   q.refId = getNextRefIdChar(queries);