Need to pull out "meta" data and remove USAS specifics

[0kl-usds]

Some initial thoughts here:

For a given hiring action store the tables/columns and meta tables/columns that will be used to generate exports in CSV format. Also store the order of these.

assessment_hurdle_export_fields
INT order
VARCHAR column_name -- e.g. applicant_middle_name
VARCHAT type ("hurdle_meta", "applicant_meta", "code", "result", "null")

Where {assessment_hurdle,applicant}_metum are:

column_name 
value
assessment_hurdle_id
applicant_id?

This should result in an extensible "export" for various TAS solutions or individual use.