fix(relations): support modelselect2 fields

in modal dialog include support for select2 multiple select fields
that are populated with values from the model (.modelselect2 and .modelselect2multiple).

assuming that no other selectors are needed,
based on /apis_core/generic/forms/__init__.py#L72

apis_core/relations/static/js/relation_dialog.js

@@ -5,7 +5,7 @@ function tohtml(item) {
 }
 document.body.addEventListener("reinit_select2", function(evt) {
     form = document.getElementById(evt.detail.value);
-    form.querySelectorAll(".listselect2").forEach(element => {
+    form.querySelectorAll(".listselect2, .modelselect2multiple, .modelselect2").forEach(element => {
         $(element).select2({
             ajax: {
                 url: $(element).data("autocomplete-light-url"),