Checks the validity of the 'source' parameter.
validate_source_param(source)
Returns TRUE
if the 'source' parameter is valid. Throws an
error if the parameter is invalid.
[mandatory] (list) A list containing datasets, each with its associated bands and statistics. The structure should follow a nested format where each dataset is a named list, each band within a dataset is also a named list, and each statistic within a band is a non-empty character string.