Is your feature request related to a problem? Please describe.
CPU metrics reported from containerised services are inaccurate.

Describe the solution you'd like
So far we only support memory cgroup-based metrics, we need to apply the same for CPU.

Steps

• Define the related data model and intake. @elastic/apm-server your assistance with that, based on Metricbeat and/or stack monitoring, would be great
• Define how and when UI will be using those
• Extend the APM agents spec accordingly

Describe alternatives you've considered
Not supporting those and keep inaccurate 🙂

Additional context
<TBD - @elastic/apm-server if you can provide evidence from such inaccuracies observed in ESS, that would be great>