Datasources: Add support for getDetDefaultQuery in variable editor (#62026)

+Cloudwatch implementation

packages/grafana-data/src/types/variables.ts

@@ -35,6 +35,11 @@ export abstract class VariableSupportBase<
   TOptions extends DataSourceJsonData = DataSourceOptionsType<DSType>
 > {
   abstract getType(): VariableSupportType;
+
+  /**
+   * Define this method in the config if you want to pre-populate the editor with a default query.
+   */
+  getDefaultQuery?(): Partial<TQuery>;
 }
 
 /**