Add unit

Add unit in both Y axis and tooltip display

Apache ECharts offer the availability to add a unit formatter.

There are two functions to provide. One for Y axis and one for the tooltip:

            yAxis: {
              axisLabel: {
                formatter: "{value} °C"
              }
            },
            tooltip: {
              formatter: function (params) {
                return (
                  Math.round(params[0].value * 100) / 100 + " °C"
                );
              }
            },