Chronos: xshards_dataset gendt_feature

[smurf-1119]

Description

add gendt_feature function to xshards_dataset

User API

shards_tmp = read_csv(file_name)
# interval = day
tsdata = XShardsTSDataset.from_xshards(shards_tmp, dt_col="datetime", target_col="value",
                                                   extra_feature_col=["extra feature"], id_col="id")
features = ['DAY',]
tsdata.gen_dt_feature(features=features)