[APM] Service instance runtime metrics

**Summary of the problem** (If there are multiple problems or use cases, prioritize them)
Currently APM agents collect various system and runtime metrics, which could help detecting resource saturation or configuration issues.
Visualizing these metrics for every agent type would make this information actionable during performance issues troubleshooting.

**User stories**

- As App Ops, I need to correlate service performance with system and runtime performance.
- As App Ops, I need to be able to identify when specific instance is performing differently than the majority of other instances.
- As App Ops, I need to quickly identify which runtime metrics are trending out of normal at the same time as service is experiencing issues.

**List known (technical) restrictions and requirements**
Has to work with different agent types and appreciate that each runtime has its own specific runtime metrics.

If in doubt, don’t hesitate to reach out to the `#observability-design` Slack channel.