parsed_labels_output: a vector of parsed labels produced by parse_labels()
field_name: the name of the field associated with the labels to use in the warning message
warn_stripped_text: logical for whether to include a note about HTML tag stripping in the message
call: the calling environment to use in the error message. The parent of calling environment by default because this check usually occurs 2 frames below the relevant context for the user
Returns
a warning message alerting specifying the duplicate labels and REDCap field affected