groups-ui: Add option to copy membership from group.

Instead of adding group as a subgroup, we now provide option
to add direct members and direct subgroups of a group to a
user group by providing an expand button in the group pill.

Fixes #32335.

web/tests/user_group_pill.test.cjs

@@ -77,6 +77,7 @@ const testers_pill = {
     group_id: testers.id,
     group_name: testers.name,
     type: "user_group",
+    show_expand_button: false,
 };
 const everyone_pill = {
     group_id: everyone.id,