Expose usedPreaggregation through REST load API in prod mode

**Is your feature request related to a problem? Please describe.**
We are heavily relying on pre-aggregation and relying on job API to force rebuilt of pre aggregation.
The API support cubes or preAggregation parameter but there is no way to know what cube or preAggregation is used by a given query.

**Describe the solution you'd like**
get `usedPreaggregation` detailed in prod mode

**Describe alternatives you've considered**
The naive alternative was to try to deduct the cube targeted using the dimension of the query but it is to reliable and force us to refresh the entire set of pre aggregation with in a cube.