[APM] Runtime metrics for all agents in the APM App

**Summary of the problem**
Most of the APM agents collect runtime metrics data which is available for customers to visualize via the apm-contrib dashboards. Java agent is the only agent that surfaces the runtime performance data on a JVMs tab for each instance of the service that is reporting. We should have a similar page for all the other agents to surface the metrics that we collect in the curated UI.

**List known (technical) restrictions and requirements**

For JVM page specifically we chose the tabular approach that shows individual instances instead of a chart with different line graphs to capture each instance because the number of instances reporting can be large. This assumption is probably true for all other agents. We should be able to surface the runtime performance captured by the agents and displayed in the APM App in a way that is compatible for each language ecosystem.

**References**

* [GDoc: APM Metrics Phase 2 Proposal](https://docs.google.com/document/d/1Kmxf0SRm-yXTv46Ut2jnmYmdIcNej87cKouG_2oQBeY/edit)
* [Meta issue: APM runtime metrics Phase 2](https://github.com/elastic/apm/issues/73)