Create an export function (to tsv format) for the aggregated counts table

It would be nice if we could export the aggregated counts as a matrix to a tsv or csv file with the aggregated item in lines and the samples in columns. We could use it like that for example:

aggregated_counts <- aggregate_counts(
  all_sample_counts = all_sample_counts,
  ref_db = ferm_veg_ref_db,
  taxonomic_level = taxonomic_level,
  functional_level = functional_level
)
export_to_delimited_file(aggregated_counts, output_file_path, sep="\t")