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-server/src/engine/core-modules/feature-flag/enums/feature-flag-key.enum.ts

@@ -9,4 +9,5 @@ export enum FeatureFlagKey {
   IsWorkflowEnabled = 'IS_WORKFLOW_ENABLED',
   IsMessageThreadSubscriberEnabled = 'IS_MESSAGE_THREAD_SUBSCRIBER_ENABLED',
   IsQueryRunnerTwentyORMEnabled = 'IS_QUERY_RUNNER_TWENTY_ORM_ENABLED',
+  IsWorkspaceFavoriteEnabled = 'IS_WORKSPACE_FAVORITE_ENABLED',
 }