Incorrect data presentation

@vmihailenco uptrace version: 1.7.6 I use prometheus+blackbox to monitor port 22 of the server, the server is healthy, the data in prometheus is 1, but uptrace shows the status data is 0 and 1

I believe the Connect the line across null points option is supposed to handle this, however it does not appear to be functioning. I suspect because connectNulls has been left off of the Go struct for the grid item params here: https://github.com/uptrace/uptrace/blob/master/pkg/metrics/grid_item.go#L126

type ChartGridItemParams struct {
	ChartKind ChartKind         `json:"chartKind"`
	Metrics   []mql.MetricAlias `json:"metrics"`
	Query     string            `json:"query"`
	// Use ColumnMap instead of MetricMap for compatibility with TableGridItem.
	ColumnMap     map[string]*MetricColumn    `json:"columnMap"`
	TimeseriesMap map[string]*TimeseriesStyle `json:"timeseriesMap"`
	Legend        *ChartLegend                `json:"legend"`
	ConnectNulls  bool                        `json:"connectNulls"`       <-- Add this
}

This should be fixed in v2.0.0