Track live metrics disabling in feature sdkstats (exporter)

[rads-1996]

Description

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• The pull request does not introduce [breaking changes]
• CHANGELOG is updated for new features, bug fixes or other significant changes.
• I have read the contribution guidelines.

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Testing Guidelines

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[Copilot]

Pull request overview

This PR updates live metrics feature tracking so that Statsbeat “live metrics” feature usage is recorded only when live metrics is explicitly disabled via the local configuration callback, rather than when enable_live_metrics() is called.

Changes:

• Remove Statsbeat live-metrics feature tracking from the enable_live_metrics() code path.
• Add Statsbeat tracking when get_quickpulse_configuration_callback() evaluates live metrics as explicitly disabled (including when Quickpulse is already off).
• Update/extend unit tests to validate the new tracking behavior and update the changelog.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
sdk/monitor/azure-monitor-opentelemetry-exporter/azure/monitor/opentelemetry/exporter/_quickpulse/_live_metrics.py	Moves Statsbeat live-metrics feature tracking from enable-time to config-disable-time within the configuration callback.
sdk/monitor/azure-monitor-opentelemetry-exporter/tests/quickpulse/test_live_metrics.py	Updates existing tests to assert Statsbeat is not tracked on enable, and adds callback-focused tests for disable tracking.
sdk/monitor/azure-monitor-opentelemetry-exporter/CHANGELOG.md	Adds an unreleased entry describing the change.