Overview

Make the query stats sampling server parameters overridable per-query via query settings (queryKnobs):

• internalQueryStatsSampleRate - sampling-based rate limiting for reads
• internalQueryStatsWriteCmdSampleRate - sampling-based rate limiting for write commands

Background

SPM-4364 added support for overriding query knobs via (P)QS, and SERVER-123044 allows passing querySettings directly as part of command invocation. Query knob exposure is opt-in, not opt-out: each knob requires a query_knob IDL annotation (pqs_settable: true, FCV-gated) and a QueryKnob cpp instance - roughly 5-10 LoC per knob per the SPM-4364 design.

The two knobs above are defined in src/mongo/db/query/query_integration_knobs.idl but are not yet settable via (P)QS.

Motivation

• Testing: allows $queryStats tests to pass these knobs per-command instead of setting cluster-wide server parameters via setParameter, enabling passthrough suite runs and removing custom ReplSetTest setups (e.g. startSet(getQueryStatsServerParameters())). Test migration is tracked as a follow-up ticket.
• Customers: allows users to ensure specific query shapes are always captured in query stats, regardless of cluster-wide sampling defaults.

Scope

• In scope: the two sampling knobs listed above.
• Out of scope: internalQueryStatsRateLimit - it is a node-global window-based throttle backed by shared state in a single RateLimiter (see src/mongo/db/query/query_stats/rate_limiting.h), so it is not applicable per query shape. Per-query internalQueryStatsSampleRate overrides take precedence over window-based limiting anyway.
• Out of scope: internalQueryStatsCacheSize - it is store-level configuration and not applicable per query shape.

Acceptance Criteria

• internalQueryStatsSampleRate and internalQueryStatsWriteCmdSampleRate can be overridden via querySettings.queryKnobs on command invocation and via PQS.
• Overrides are FCV-gated consistently with the query knob framework.
• Unit tests and/or jstests cover the new overrides.