Use portfolio_role.id for updating primary point of contact.

Our forms should rely on role IDs for displaying user information on the
portfolio page. This way they are decoupled from user table data and can
eventually rely on invitation user data where an invitation has been
sent but a user does not exist yet.

templates/fragments/admin/change_ppoc.html

@@ -22,7 +22,7 @@
     <div class='form-col form-col--half'>
       {{
         OptionsInput(
-          assign_ppoc_form.user_id
+          assign_ppoc_form.role_id
         )
       }}
     </div>