Restore original urgency to feature flag endpoints

What does this MR do and why?

Originally, the urgency of the feature flag endpoint (GET /api/:version/feature_flags/unleash/:project_id/client/features) was default (<1s), however, it was tightened in Increasing request urgency for unleash features... (!113723 - merged) to medium (<0.5s). Because of this, groupenvironments's error budget dashboard is at very close to fail the target.

While we understand that a shorter duration is always preferred, we have already exhausted low-hanging fruits to optimize the endpoints (e.g. #276406 (closed)). So the next optimization could become a big one, such as putting data into object storage and proxying the request at Workhorse, which would take at least a half year roughly estimating. However, the feature flag category was put under maintenance mode due to the recent re-org, it's quite difficult for us to afford the significant effort with developing and optimizing our main focus areas (e.g. Kubernetes Integration, KAS, agentk, etc).

Therefore, we wonder if groupscalability can accept this request to restore the original urgency default to the endpoint.

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