chore: Enhance contact merge action for identified users (#4886)

- Discard conflicting keys 
- Do not merge if there is already an identified contact

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

app/helpers/widget_helper.rb

@@ -0,0 +1,9 @@
+module WidgetHelper
+  def build_contact_inbox_with_token(web_widget, additional_attributes = {})
+    contact_inbox = web_widget.create_contact_inbox(additional_attributes)
+    payload = { source_id: contact_inbox.source_id, inbox_id: web_widget.inbox.id }
+    token = ::Widget::TokenService.new(payload: payload).generate_token
+
+    [contact_inbox, token]
+  end
+end