Add ability to bypass default vector oversampling and rescoring

It is now possible to set a default oversample & rescore parameter for a given quantized index: #124581

However, it is possible that at query time, users may want to bypass that default oversampling and disable oversampling for particular queries.

Consequently, we should add a specialized floating point value for query time rescore_vector parameters.

I suggest that the value oversample: 0 indicates no oversampling is desired, and will override any index level defaults for oversampling.

Provide feedback