Add workspace favorites behind feature flag (#6904)

- make member nullable on favorites
- add potential relation with view entity
- add a new type of favorite list in front : workspace favorite
- build a new component for retrieving workspace favorite to display +
refacto the existing one

Bonus:
- removing activities seed since this is deprecated

packages/twenty-front/src/modules/workspace/types/FeatureFlagKey.ts

@@ -8,4 +8,5 @@ export type FeatureFlagKey =
   | 'IS_CRM_MIGRATION_ENABLED'
   | 'IS_FREE_ACCESS_ENABLED'
   | 'IS_MESSAGE_THREAD_SUBSCRIBER_ENABLED'
-  | 'IS_WORKFLOW_ENABLED';
+  | 'IS_WORKFLOW_ENABLED'
+  | 'IS_WORKSPACE_FAVORITE_ENABLED';