Add setting for contact roster name

And only exchange contacts when ejabberd integration is enabled

app/views/admin/settings/services/_ejabberd.html.erb

@@ -18,5 +18,13 @@
         value: Setting.ejabberd_admin_url,
         class: "w-full", disabled: true %>
     <% end %>
+    <%= render FormElements::FieldsetComponent.new(
+          title: "Contact roster name",
+          description: "Used when exchanging contacts after signup from invitation"
+        ) do %>
+      <%= f.text_field :ejabberd_buddy_roster,
+        value: Setting.ejabberd_buddy_roster,
+        class: "w-full" %>
+    <% end %>
   <% end %>
 </ul>