Server Response Deserialization Time Metric on Broker Side

**Why do we need this?**
We are observing a significant difference in the `SCATTER_GATHER` timer metric value at the broker layer and the `TOTAL_QUERY_TIME` timer metric value at the server layer.

Additional metrics across each phase at the broker layer would be helpful for debugging it.

Start by tracing the broker-side SCATTER_GATHER timer and the server-side TOTAL_QUERY_TIME timer through the query paths. Identify the response deserialization phase and define the additional broker metric needed to compare it with server timing; done means the metric is exposed and the phase difference can be diagnosed.

Written by the indexing model from the issue text.