Function to process site ID value from pscis_crossing_id and my_crossing_reference
Source:R/fpr_tidy_assign_site_id.R
fpr_tidy_assign_site_id.Rd
Intended for processing field data from digital form in which only one value should be provided. It checks if the dataframe has both 'pscis_crossing_id' and 'my_crossing_reference' values, or none of them. If any rows violate these rules, it returns an error that prints out a simplified dataframe with violating rows.