augment_shifted: add a shifted value
In rte-antares-rpackage/antaDraft: clean and validate entsoe datasets

add a shifted value to an existing dataset.

1	augment_shifted(x, col, hour_shift = -1, summary_colname = "summary")

`x`	dataset
`col`	column name of the measure to be aggregated and lagged
`hour_shift`	lag as a number of hours
`summary_colname`	column name containing results from `augment_process_summary`

load_dir <- system.file(package = "antaDraft",
  "data_sample/load_sample_2017")

load_data <- anta_load(data_dir = load_dir )
load_data <- augment_validation(data = load_data)
head(load_data)

aggregated_db <- agg_data(load_data)
aggregated_db <- augment_validation(aggregated_db)
aggregated_db <- data_correct_with_rules(aggregated_db)
aggregated_db <- augment_process_summary(aggregated_db)
aggregated_db <- augment_holiday(aggregated_db)
aggregated_db <- augment_seasons_id(aggregated_db)
aggregated_db <- augment_daylight(aggregated_db)
aggregated_db <- augment_daily(aggregated_db, col = "CTY", decay = 1)
aggregated_db <- augment_shifted(aggregated_db, col = "CTY", hour_shift = -1)
head(aggregated_db)