Add documentation for tracing.sampling-ratio configuration property

[hashroute3]

Description

Document the otel.tracing.sampling-ratio configuration property in the OpenTelemetry tracing documentation. This property already exists in the Airlift OpenTelemetryConfig class and controls the ratio of traces that are sampled and exported, but was not documented in the Trino docs.

Additional context and related issues

When tracing is enabled with the default sampling ratio of 1 (100%), high-traffic Trino deployments can generate excessive trace events, causing high load and cost on observability backends (e.g. Honeycomb, Jaeger). The workaround today is running an OpenTelemetry collector sidecar with sampling configuration, which adds unnecessary operational complexity.

Documenting otel.tracing.sampling-ratio allows users to reduce trace volume directly in Trino's config.properties without external workarounds.

The property is confirmed visible in Trino bootstrap logs:

Bootstrap    otel.tracing.sampling-ratio    1.0    1.0

Release notes

(x) This is not user-visible or is docs only, and no release notes are required.
( ) Release notes are required. Please propose a release note for me.
( ) Release notes are required, with the following suggested text:

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[hashroute3]

@ebyhr Thank you for the review! I’ve addressed all the feedback you shared.