Configures the Stacked series.
The optional stack group name.
group option is supported for the Bar and Column series.
"normal" | "100%"
The type of stack to plot.
The following types are supported:
"normal"—The value of the stack is the sum of all points in the category (or group).
"100%"—The value of the stack is always 100% (1.00). Points within the category (or group) are represented in percentage.