Link Person Certificates to certificate master

[Robin481]

Now after #784, instead of entering free form text people should choose their certificates from the central master list.

However, we need to handle old data that was entered as free form. Therefore, the free form text field should still be an option, we are just not gonna display it as the primary option.

In addition, when a certificate is selected from the master list, we can also display its PCTS value to the person.

TODO:

• Add a dropdown option to the person certificate view
• List all certificates from the master list there and let them be searchable (same as person-search)
• Display PCTS values when it is selected from the master list
• Display the free text option as a backup (maybe some form of checkbox enter as free form text instead or similar)
• Tests of course 🍏