Create a server metric to represent the number of bytes written to both data tables and index tables, quantized to a configureable Unit size.

Currently we have similar metrics that only use data table bytes (docUnitsRead/docUnitsWritten), or index table bytes (idxEntryBytesRead/idxEntryBytesWritten).

Proposal is to add a new metric:
totalUnitsWritten

and one new configuration parameter, totalUnitWriteSizeBytes

Additionally, a timestamp field "localTime" will be added to each database BSONArray in the output for the operationMetrics aggregation stage, as per InTel request.