This change adds the following 3 stream process-level throughput metrics on mongoS:

• *metrics.changeStreams.cursor.docsReturned* (counter): Shows the cumulative number of returned change events by all change stream cursors.
• *metrics.changeStreams.cursor.bytesReturned* (counter): Shows the cumulative amount in bytes returned by all change stream cursors.
• *metrics.changeStreams.cursor.batchesReturned* (counter): Shows the cumulative number of batches returned by all change streams.

  Description of Linked Ticket

  Add change stream specific throughput metrics on mongoS (see project design document section "Decision: Process-Level Change Stream Cursor Metrics / Throughput"):

• metrics.changeStreams.cursor.docsReturned(already exists for query stats)
• metrics.changeStreams.cursor.bytesReturned
• metrics.changeStreams.cursor.batchesReturned(already exists for query stats)

Design notes:

• The docsReturned, bytesReturned, and batchesReturned should come from mongoS (router) pipeline creating the batches.