check_summary_params: Check input parameters for `summarise_scores()`

Description

A helper function to check the input parameters for score().

check_summary_params(scores, by, relative_skill, baseline, metric)

scores: A data.table of scores as produced by score().
by: character vector with column names to summarise scores by. Default is NULL, meaning that the only summary that takes is place is summarising over samples or quantiles (in case of quantile-based forecasts), such that there is one score per forecast as defined by the unit of a single forecast (rather than one score for every sample or quantile). The unit of a single forecast is determined by the columns present in the input data that do not correspond to a metric produced by score(), which indicate indicate a grouping of forecasts (for example there may be one forecast per day, location and model). Adding additional, unrelated, columns may alter results in an unpredictable way.
relative_skill: logical, whether or not to compute relative performance between models based on pairwise comparisons. If TRUE (default is FALSE), then a column called 'model' must be present in the input data. For more information on the computation of relative skill, see pairwise_comparison(). Relative skill will be calculated for the aggregation level specified in by.
baseline: character string with the name of a model. If a baseline is given, then a scaled relative skill with respect to the baseline will be returned. By default (NULL), relative skill will not be scaled with respect to a baseline model.
metric: Deprecated in 1.1.0. Use relative_skill_metric instead.