chore(traces): Register flag for cross event querying (#103987)

Register a new flag for controlling the rollout of cross event querying
on the traces page.

Ticket: EXP-617

Author: nsdeschenes

src/sentry/features/temporary.py

@@ -607,6 +607,8 @@ def register_temporary_features(manager: FeatureManager) -> None:
     manager.add("organizations:tracemetrics-stats", OrganizationFeature, FeatureHandlerStrategy.FLAGPOLE, api_expose=True)
     # Enable trace metrics in trace view UI
     manager.add("organizations:tracemetrics-traceview-ui", OrganizationFeature, FeatureHandlerStrategy.FLAGPOLE, api_expose=True)
+    # Enable traces page cross event querying
+    manager.add("organizations:traces-page-cross-event-querying", OrganizationFeature, FeatureHandlerStrategy.FLAGPOLE, api_expose=True)
     # Enable downsampled date page filter
     manager.add("organizations:downsampled-date-page-filter", OrganizationFeature, FeatureHandlerStrategy.FLAGPOLE, api_expose=True)