Feature: add faceting to the person search collection

[sennierer]

in the typesense index we need two new array fields that allow for faceting:

• "Funktion": PersonInstitutionRelation.name -> thats the kind of role somebody had in an institution (eg a court).
• "Amt": PersonInstitution.related_institution.name -> thats the institution somebody fulfilled that role in (eg the court)

Given that the current index uses the apis field names we should stick with that tradition and name the fields accordingly