[Kubernetes] Change Memory and Cpu calculation to use allocatable metric

[gizas]

Currently in metricbeat we use capacity metric calculate allocatable memory and cpu. See for memory and for cpu.

The k8s v1 api describes the difference between capacity and allocatable. This issue is to track the work needed to replace Status.Capacity to Status.Allocatable and use the allocatable metrics in our calculations.

Definition of done:

• Update the code
• Test e2e that relevant mettrics like contianer.cpu.usage.node.pct and container.memory.usage.node.pct are being poplated correctly.