Retrieves a custom field with a given name, or creates one if it doesn't exist.
The findOrCreateExtendedField() function returns a Promise
that resolves when the specified custom field is found or created.
Successful calls to findOrCreateExtendedField() always return an
extended field,
which can be passed to subsequent function calls.
To find an existing extended field without potentially creating a new one, use
getExtendedField() or
queryExtendedFields().
Note:
Only visitors with
Manage Contacts permissions
can find or create extended fields.
You can override the permissions by setting the suppressAuth option to true.
Custom field to find or create.
Authorization options.