feat(workflow_engine): add workflow-engine-ui feature flag (#81688)

Adds a new `workflow-engine-ui` feature flag to control the frontend UI
rollout for ACI (see `#proj-alerts-create-issues`).

Author: natemoo-re

src/sentry/features/temporary.py

@@ -539,6 +539,8 @@ def register_temporary_features(manager: FeatureManager):
     manager.add("organizations:widget-viewer-modal-minimap", OrganizationFeature, FeatureHandlerStrategy.FLAGPOLE, api_expose=True)
     # Enabled unresolved issue webhook for organization
     manager.add("organizations:webhooks-unresolved", OrganizationFeature, FeatureHandlerStrategy.OPTIONS, api_expose=True)
+    # Enable new workflow_engine UI (see: alerts create issues)
+    manager.add("organizations:workflow-engine-ui", OrganizationFeature, FeatureHandlerStrategy.FLAGPOLE, api_expose=True)
     # Enable EventUniqueUserFrequencyConditionWithConditions special alert condition
     manager.add("organizations:event-unique-user-frequency-condition-with-conditions", OrganizationFeature, FeatureHandlerStrategy.FLAGPOLE, api_expose=True)
     # Use spans instead of transactions for dynamic sampling calculations. This will become the new default.