feat(nextjs-insights): Add feature flag (#89598)

- part of [TET-294: Feature flag, page
skeleton](https://linear.app/getsentry/issue/TET-294/feature-flag-page-skeleton)

Author: ArthurKnaus

src/sentry/features/temporary.py

@@ -188,6 +188,8 @@ def register_temporary_features(manager: FeatureManager):
     manager.add("organizations:navigation-sidebar-v2", OrganizationFeature, FeatureHandlerStrategy.FLAGPOLE, api_expose=True)
     manager.add("organizations:navigation-sidebar-v2-banner", OrganizationFeature, FeatureHandlerStrategy.FLAGPOLE, api_expose=True)
     manager.add("organizations:new-page-filter", OrganizationFeature, FeatureHandlerStrategy.FLAGPOLE, default=True, api_expose=True)
+    # Enable access to NextJS specific insights
+    manager.add("organizations:nextjs-insights", OrganizationFeature, FeatureHandlerStrategy.FLAGPOLE, api_expose=True)
     # Drop obsoleted status changes in occurence consumer
     manager.add("organizations:occurence-consumer-prune-status-changes", OrganizationFeature, FeatureHandlerStrategy.FLAGPOLE, api_expose=False)
     # Enable User Feedback v1