chore(issue-details): Don't default to false for streamlined ui

[roggenkemper]

with #87336 will allow us to start opting users into the new experience. Returns None instead of False so that the frontend can determine if we show the new UI or not

[codecov]

❌ 1 Tests Failed:

Tests completed	Failed	Passed	Skipped
24451	1	24450	299

View the top 1 failed test(s) by shortest run time

tests.sentry.workflow_engine.migration_helpers.test_migrate_alert_rule.SinglePointOfEntryTest::test_spe_create

Stack Traces | 3.14s run time

#x1B[1m#x1B[.../workflow_engine/migration_helpers/test_migrate_alert_rule.py#x1B[0m:1330: in test_spe_create
    dual_write_alert_rule(self.metric_alert)
#x1B[1m#x1B[.../workflow_engine/migration_helpers/alert_rule.py#x1B[0m:593: in dual_write_alert_rule
    migrate_alert_rule(alert_rule)
#x1B[1m#x1B[.../workflow_engine/migration_helpers/alert_rule.py#x1B[0m:552: in migrate_alert_rule
    workflow_name = get_workflow_name(alert_rule)
#x1B[1m#x1B[.../workflow_engine/migration_helpers/utils.py#x1B[0m:53: in get_workflow_name
    description = get_action_description(action) + ", "
#x1B[1m#x1B[.../workflow_engine/migration_helpers/utils.py#x1B[0m:23: in get_action_description
    if action.target:
#x1B[1m#x1B[.../incidents/models/alert_rule.py#x1B[0m:476: in target
    return user_service.get_user(user_id=int(self.target_identifier))
#x1B[1m#x1B[.../services/user/service.py#x1B[0m:201: in get_user
    return get_user(user_id)
#x1B[1m#x1B[.../rpc/caching/service.py#x1B[0m:76: in __call__
    return self.get_one(object_id)
#x1B[1m#x1B[.../rpc/caching/service.py#x1B[0m:109: in get_one
    return _consume_generator(self.resolve_from(object_id, values))
#x1B[1m#x1B[.../rpc/caching/impl.py#x1B[0m:24: in _consume_generator
    g.send(None)
#x1B[1m#x1B[.../rpc/caching/service.py#x1B[0m:99: in resolve_from
    r = self.cb(i)
#x1B[1m#x1B[.../services/user/service.py#x1B[0m:320: in get_user
    users = user_service.get_many(filter={"user_ids": [user_id]})
#x1B[1m#x1B[.../hybridcloud/rpc/service.py#x1B[0m:354: in remote_method
    return dispatch_remote_call(
#x1B[1m#x1B[.../hybridcloud/rpc/service.py#x1B[0m:476: in dispatch_remote_call
    return remote_silo_call.dispatch(use_test_client)
#x1B[1m#x1B[.../hybridcloud/rpc/service.py#x1B[0m:511: in dispatch
    serial_response = self._send_to_remote_silo(use_test_client)
#x1B[1m#x1B[.../hybridcloud/rpc/service.py#x1B[0m:572: in _send_to_remote_silo
    response = self._fire_test_request(headers, data)
#x1B[1m#x1B[.../hybridcloud/rpc/service.py#x1B[0m:631: in _fire_test_request
    in_test_assert_no_transaction(
#x1B[1m#x1B[.../db/postgres/transactions.py#x1B[0m:101: in in_test_assert_no_transaction
    assert not hybrid_cloud.simulated_transaction_watermarks.connection_transaction_depth_above_watermark(
#x1B[1m#x1B[31mE   AssertionError: remote service method to .../rpc/user/get_many/ called inside transaction!  Move service calls to outside of transactions.#x1B[0m

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