Improve metric collection and reporting

[ruflin]

Currently Beats report all metrics in one document. To report metrics more granular through different documents several changes to Beats metric collection and monitoring reporting are needed. This issue is to track the changes.

• Introduce namespace to make collection of metrics to different API endpoints possible. Add namespaces to monitoring registry #6836
• Report state stats: Implement state reporting for Beats #7521
• Add support for gauge metric types in Metricbeat to automate gauge detection on reporting
• Update existing monitoring output and remove module specific stats as they are reported separately
• Support reporting of arrays in Monitoring or manual definition on how data should be reported.

[botelastic]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.