chore(issue-stream): Register feature flag for upcoming new assignee dropdown trigger (#70972)

Title

* [SOA
PR](https://github.com/getsentry/sentry-options-automator/pull/1435)

src/sentry/conf/server.py

@@ -1627,6 +1627,8 @@ SENTRY_FEATURES: dict[str, bool | None] = {
     "organizations:issue-search-allow-postgres-only-search": False,
     # Whether to make a side/parallel query against events -> group_attributes when searching issues
     "organizations:issue-search-group-attributes-side-query": False,
+    # Enable the new assignee dropdown trigger on issue stream
+    "organizations:issue-stream-new-assignee-dropdown-trigger": False,
     # Enable the updated empty state for issues
     "organizations:issue-stream-empty-state": False,
     # Enable new events graph design for issue stream

src/sentry/features/temporary.py

@@ -95,6 +95,7 @@ def register_temporary_features(manager: FeatureManager):
     manager.add("organizations:issue-search-allow-postgres-only-search", OrganizationFeature, FeatureHandlerStrategy.REMOTE)
     manager.add("organizations:issue-search-group-attributes-side-query", OrganizationFeature, FeatureHandlerStrategy.REMOTE)
     manager.add("organizations:issue-stream-empty-state", OrganizationFeature, FeatureHandlerStrategy.REMOTE)
+    manager.add("organizations:issue-stream-new-assignee-dropdown-trigger", OrganizationFeature, FeatureHandlerStrategy.OPTIONS)
     manager.add("organizations:issue-stream-new-events-graph", OrganizationFeature, FeatureHandlerStrategy.OPTIONS)
     manager.add("organizations:issue-stream-performance", OrganizationFeature, FeatureHandlerStrategy.REMOTE)
     manager.add("organizations:large-debug-files", OrganizationFeature, FeatureHandlerStrategy.INTERNAL)