Propose new conventions

Area(s)

area:k8s

Is your change request related to a problem? Please describe.

As part of the K8s SemConv stability work we need to define k8s container resource related metrics that are already in use by the Opentelemetry Collector.

Related to #1032

Describe the solution you'd like

The existing metrics in use that we need to define as semantic conventions are the following:

k8s.container.cpu_request
k8s.container.cpu_limit
k8s.container.memory_request
k8s.container.memory_limit
k8s.container.storage_request
k8s.container.storage_limit
k8s.container.ephemeralstorage_request
k8s.container.ephemeralstorage_limit
k8s.container.restarts
k8s.container.ready