Remove IS_APPLICATION_INSTALLATION_FROM_TARBALL_ENABLED feature flag (#18520)

## Summary
- Removes the `IS_APPLICATION_INSTALLATION_FROM_TARBALL_ENABLED` feature
flag, consolidating tarball-based app installation under the existing
`IS_APPLICATION_ENABLED` flag
- Removes the runtime feature flag check in `runWorkspaceMigration`
resolver (the `@RequireFeatureFlag(IS_APPLICATION_ENABLED)` decorator
already gates this endpoint)
- Cleans up related integration test setup/teardown and mock feature
flag maps

## Test plan
- [ ] Verify tarball-based app installation still works when
`IS_APPLICATION_ENABLED` is true
- [ ] Verify app installation is blocked when `IS_APPLICATION_ENABLED`
is false
- [ ] Run `failing-install-application.integration-spec.ts` to confirm
it passes without the removed flag


Made with [Cursor](https://cursor.com)

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

@@ -241,7 +241,6 @@ describe('WorkspaceEntityManager', () => {
         IS_COMMAND_MENU_ITEM_ENABLED: false,
         IS_NAVIGATION_MENU_ITEM_ENABLED: false,
         IS_NAVIGATION_MENU_ITEM_EDITING_ENABLED: false,
-        IS_APPLICATION_INSTALLATION_FROM_TARBALL_ENABLED: false,
         IS_RECORD_PAGE_LAYOUT_EDITING_ENABLED: false,
         IS_MARKETPLACE_ENABLED: false,
         IS_DATE_TIME_WHOLE_DAY_FILTER_ENABLED: false,