Building on the work in SERVER-134091, we should also track (via histograms) the number of keys written to index(es) (including deletes) as well as the number of bytes written to index(es), with attributes for the start phase and the outcome. This may require refactoring in order to track these written keys/bytes across the entire index build. N.B.: the only phases that write to the index(es) itself are the load phase and the drain writes phase.

This should also be accompanied by updates including these metrics to a single coherent log message that should be emitted on every index build termination.