ref(perf): add a feature flag for the new span schema (#83532)

This feature flag will control whether the performance UI uses the new
span schema or the legacy one.

Closes getsentry/team-performance#54.

src/sentry/features/temporary.py

@@ -266,6 +266,8 @@ def register_temporary_features(manager: FeatureManager):
     manager.add("organizations:performance-metrics-backed-transaction-summary", OrganizationFeature, FeatureHandlerStrategy.FLAGPOLE, api_expose=False)
     # Enable the UI for displaying mobile performance score
     manager.add("organizations:performance-mobile-perf-score-ui", OrganizationFeature, FeatureHandlerStrategy.FLAGPOLE, api_expose=False)
+    # Use the new OTel-influenced span schema across the performance product
+    manager.add("organizations:performance-new-span-schema", OrganizationFeature, FeatureHandlerStrategy.FLAGPOLE, api_expose=True)
     # Enable new trends
     manager.add("organizations:performance-new-trends", OrganizationFeature, FeatureHandlerStrategy.FLAGPOLE, api_expose=True)
     # Enable updated landing page widget designs