Create a feature flag for dashboards v2 (#15601)

Prevent users from creating v2 chart types via the api.
Only created unit tests and not integration tests (since it's not that
important, and the v2 will be released soon), but tested via the api
playground.

packages/twenty-server/src/engine/twenty-orm/entity-manager/workspace-entity-manager.spec.ts

@@ -138,6 +138,7 @@ describe('WorkspaceEntityManager', () => {
         IS_PUBLIC_DOMAIN_ENABLED: false,
         IS_EMAILING_DOMAIN_ENABLED: false,
         IS_WORKFLOW_RUN_STOPPAGE_ENABLED: false,
+        IS_DASHBOARD_V2_ENABLED: false,
       },
       eventEmitterService: {
         emitMutationEvent: jest.fn(),
@@ -163,6 +164,8 @@ describe('WorkspaceEntityManager', () => {
         IS_MESSAGE_FOLDER_CONTROL_ENABLED: false,
         IS_PUBLIC_DOMAIN_ENABLED: false,
         IS_EMAILING_DOMAIN_ENABLED: false,
+        IS_WORKFLOW_RUN_STOPPAGE_ENABLED: false,
+        IS_DASHBOARD_V2_ENABLED: false,
       },
       permissionsPerRoleId: {},
     } as WorkspaceDataSource;