Tests whether the first column of a data frame contains either
non-numeric values (default) or any of the potential_keywords supplied.
is_key_column_present(data_table, potential_keywords = NULL)A logical scalar: TRUE if the key column is valid, otherwise throws
an error with a descriptive message.
A data frame with a key column in its first position.
Optional character vector of keywords expected in
the key column. Defaults to NULL, in which case the function only asserts
that the first column is not numeric.