Support split ratio for ts forecasting task
Created by: Dreamlone
The split factor for the time series is now ignored. There is a need to implement time series in-sample forecasting to use this info during validation
_sample_split_ratio_for_tasks = {
TaskTypesEnum.classification: 0.8,
TaskTypesEnum.regression: 0.8,
TaskTypesEnum.ts_forecasting: 0.5
}