customLabel
Currently, only for Pie Chart.
| Type | Default | 
|---|---|
| num Function(NumericData, int?)? | domain value | 
| String Function(OrdinalData, int?)? | domain value | 
| DateTime Function(TimeData, int?)? | domain value | 
customLabel: (numericData, index) {
    return '${numericData.domain}: ${numericData.measure} kg';
},
customLabel: (ordinalData, index) {
    return '${ordinalData.domain}: ${ordinalData.measure}';
},
customLabel: (timeData, index) {
    return '${timeData.domain}: ${timeData.measure}';
},