Respond with not found on missing tenants

Just like we respond with "not found" for any other record. This
improves the user experience because with the "Not found" error message
people realize the URL is wrong instead of thinking that they broke the
application.

config/application.rb

@@ -48,6 +48,7 @@ module Consul
 
     # Handle custom exceptions
     config.action_dispatch.rescue_responses["FeatureFlags::FeatureDisabled"] = :forbidden
+    config.action_dispatch.rescue_responses["Apartment::TenantNotFound"] = :not_found
 
     # Store uploaded files on the local file system (see config/storage.yml for options).
     config.active_storage.service = :local

spec/system/multitenancy_spec.rb

@@ -173,4 +173,12 @@ describe "Multitenancy", :seed_tenants do
       expect(page).not_to have_css "html.tenant-public"
     end
   end
+
+  scenario "Shows the not found page when accessing a non-existing tenant", :show_exceptions do
+    with_subdomain("jupiter") do
+      visit root_path
+
+      expect(page).to have_title "Not found"
+    end
+  end
 end