feat (ee): APIs to configure an auto assignment limit for inboxes (#4672)

Co-authored-by: Pranav Raj S <pranav@chatwoot.com>

enterprise/app/controllers/enterprise/api/v1/accounts/inboxes_controller.rb

@@ -0,0 +1,9 @@
+module Enterprise::Api::V1::Accounts::InboxesController
+  def inbox_attributes
+    super + ee_inbox_attributes
+  end
+
+  def ee_inbox_attributes
+    [auto_assignment_config: [:max_assignment_limit]]
+  end
+end