Allow Using Target Median Encoding for Cycles and Seasonals

[antoinecarme]

PyAF uses target mean encoding for these components.

Seasonal_Hour[17] = mean(filter(trend_residue , hour = 17))

Target median encoding is more robust.

Seasonal_Hour[17] = median(filter(trend_residue , hour = 17))

Add an option to control this behavior.

Will target median be the default behavior ?

[antoinecarme]

Closing