Cloudwatch: Change deprecated errorsource references (#97827)

This has been failing to compile, bringing down a _lot_ of tests along with it (notably the entire pkg/tests dir).
The `experimental/errorsource` package was deprecated, so the recommended replacement was used.

pkg/tsdb/cloudwatch/time_series_query.go

@@ -34,7 +34,7 @@ func (e *cloudWatchExecutor) executeTimeSeriesQuery(ctx context.Context, req *ba
 
 	instance, err := e.getInstance(ctx, req.PluginContext)
 	if err != nil {
-		errorsource.AddErrorToResponse(req.Queries[0].RefID, resp, err)
+		resp.Responses[req.Queries[0].RefID] = backend.ErrorResponseWithErrorSource(err)
 		return resp, nil
 	}