chore(discover-migration): Make ff for exposing migrated discover queries in explore (#95435)

Preparing for discover -> explore migration by just setting up feature
flags. Setting up this feature flag to expose migrated discover queries
in the explore saved queries table. This will be used in the backend (to
return the migrated queries from the explore saved queries endpoint if
they have the feature flag) and frontend (to ensure we are displaying
the information/warnings that we'll need once queries are migrated)

Author: nikkikapadia

src/sentry/features/temporary.py

@@ -124,6 +124,8 @@ def register_temporary_features(manager: FeatureManager):
     manager.add("organizations:escalating-issues-v2", OrganizationFeature, FeatureHandlerStrategy.INTERNAL, api_expose=False)
     # Enable emiting escalating data to the metrics backend
     manager.add("organizations:escalating-metrics-backend", OrganizationFeature, FeatureHandlerStrategy.INTERNAL, api_expose=False)
+    # Enable returning the migrated discover queries in explore saved queries
+    manager.add("organizations:expose-migrated-discover-queries", OrganizationFeature, FeatureHandlerStrategy.FLAGPOLE, api_expose=True)
     # Enable GenAI features such as Autofix and Issue Summary
     manager.add("organizations:gen-ai-features", OrganizationFeature, FeatureHandlerStrategy.FLAGPOLE, api_expose=True)
     # Enable the 'generate me a query' functionality on the explore > traces page