Feature request: continous color scale legend for `biplot`

[wbvguo]

Dear PCAtools developer,

thanks for maintaining this tool. I tried to assign a continuous variable to augment colby in function biplot, however, it looks like the color legend is discretized. May I ask if we could support a continuous color scale legend?

biplot(pcaobj, x = "PC4", y = "PC1", colby = "Age", lab = NULL, legendPosition = 'top')

Thanks!