chore: ability to run Chatwoot as API only server (#2344)

- Ability to run chatwoot as an API only server
- Removes action cable testing gem since it is merged to rails 6

spec/controllers/dashboard_controller_spec.rb

@@ -17,4 +17,18 @@ describe '/app/login', type: :request do
       ENV['DEFAULT_LOCALE'] = 'en'
     end
   end
+
+  # Routes are loaded once on app start
+  # hence Rails.application.reload_routes! is used in this spec
+  # ref : https://stackoverflow.com/a/63584877/939299
+  context 'with CW_API_ONLY_SERVER true' do
+    it 'returns 404' do
+      ENV['CW_API_ONLY_SERVER'] = 'true'
+      Rails.application.reload_routes!
+      get '/app/login'
+      expect(response).to have_http_status(:not_found)
+      ENV['CW_API_ONLY_SERVER'] = nil
+      Rails.application.reload_routes!
+    end
+  end
 end