Error Budget improvement: POST /api/:version/chat/completions

Problem

Currently, the score of groupduo chat Error Budget dashboard is less than 60.0, which means our feature is not performing well. We should identify the root cause and the fix it.

According to the Rails Requests Apdex, requests to the POST /api/:version/chat/completions is slower than the default threshold (< 1 sec).

Proposal

This endpoint is used for evaluations by groupai model validation group, hence this is not user-facing latency. We should set it to urgency :low (< 5 sec) or ignoring it completely.