Add no value column on Kanban (#6252)

<img width="1512" alt="image"
src="https://github.com/user-attachments/assets/9fcdd5ca-4329-467c-ada8-4dd5d45be259">

Open questions:
- the Tag component does not match Figma in term of style and API for
"transparent" | "outline". We need to discuss with @Bonapara what is the
desired behavior here
- right now opportunity.stage is not nullable. We need to discuss with
@FelixMalfait and @Bonapara what we want here. I would advocate to make
a it nullable for now until we introduce settings on select fields.
custom select are nullable and it could be confusing for the user

Follow up:
- enhance tests on Tags
- add story to cover the No Value column on record board

packages/twenty-front/src/modules/object-metadata/utils/formatFieldMetadataItemAsFieldDefinition.ts

@@ -40,6 +40,7 @@ export const formatFieldMetadataItemAsFieldDefinition = ({
     targetFieldMetadataName:
       field.relationDefinition?.targetFieldMetadata?.name ?? '',
     options: field.options,
+    isNullable: field.isNullable,
   };
 
   return {