Enable workflow testing + fix header (#8512)

- clean execution header
- enable test on workflows + add snack bar
- display snack bar error if workflow cannot be tested

Behaviour still need to be validated by @Bonapara 
<img width="880" alt="Capture d’écran 2024-11-15 à 12 16 36"
src="https://github.com/user-attachments/assets/1dab0c3b-157c-449f-aee7-4c8cf2e369a6">
<img width="880" alt="Capture d’écran 2024-11-15 à 12 16 48"
src="https://github.com/user-attachments/assets/16279611-0a58-4fe6-b117-0192714a6d5c">

packages/twenty-front/src/modules/ui/layout/show-page/components/ShowPageAddButton.tsx

@@ -15,6 +15,7 @@ import { useDropdown } from '@/ui/layout/dropdown/hooks/useDropdown';
 import { SHOW_PAGE_ADD_BUTTON_DROPDOWN_ID } from '@/ui/layout/show-page/constants/ShowPageAddButtonDropdownId';
 
 import { CoreObjectNameSingular } from '@/object-metadata/types/CoreObjectNameSingular';
+import { isWorkflowSubObjectMetadata } from '@/object-metadata/utils/isWorkflowSubObjectMetadata';
 import { Dropdown } from '../../dropdown/components/Dropdown';
 import { DropdownMenu } from '../../dropdown/components/DropdownMenu';
 
@@ -54,7 +55,8 @@ export const ShowPageAddButton = ({
     activityTargetObject.targetObjectNameSingular ===
       CoreObjectNameSingular.Task ||
     activityTargetObject.targetObjectNameSingular ===
-      CoreObjectNameSingular.Note
+      CoreObjectNameSingular.Note ||
+    isWorkflowSubObjectMetadata(activityTargetObject.targetObjectNameSingular)
   ) {
     return;
   }