Summary

Add process-level histograms for change-stream cursor options batchSize and maxTimeMS.

Background

Design doc: "Design: Extend ChangeStream Metrics", section "Decision: Process-Level Feature Usage
Counters" (cursor option histograms subsection).

Scope of Work

* Implement and wire up (names already registered in
src/mongo/otel/metrics/metric_names.h):
** serverStatus.metrics.changeStreams.option.cursor.batchSize (histogram; buckets: 0, 1, 10,
100, 1000, 10000) — kChangeStreamOptionCursorBatchSize
** serverStatus.metrics.changeStreams.option.cursor.maxTimeMS (histogram; 1-2-5 series
buckets) — kChangeStreamOptionCursorMaxTimeMS
* Update once per batch (getMore or aggregate excluding batchSize=0); only count when
the option was explicitly specified (except maxTimeMS equal to the current default, which
should still be counted).
* Implement on both mongoD and mongoS.

Acceptance Criteria

* Both histograms populate correctly for aggregate and getMore commands specifying the
respective option, on both mongoD and mongoS.
* Unspecified options are not counted (except the maxTimeMS default case).
* Unit test coverage for bucket boundaries.

Related Files

* src/mongo/db/commands/query_cmd/run_aggregate.cpp
* src/mongo/db/commands/query_cmd/getmore_cmd.cpp
* src/mongo/s/query/exec/cluster_client_cursor_impl.cpp