finalize_nbeats: Function to select best N-BEATS based on chosen metric
In vidarsumo/sumots: Helper functions for Sumo Analytics

Function to select best N-BEATS based on chosen metric

1	finalize_nbeats(accuracy_table, id, freq, recipe, splits, metric = "rmse")

`accuracy_table`	Table from tune_nbeats()
`id`	A quoted column name that tracks the GluonTS FieldName "item_id"
`freq`	A pandas timeseries frequency such as "5min" for 5-minutes or "D" for daily.
`recipe`	GluonTS recipe
`metric`	The metric used to choose the best model
`split`	objects