Associate K8s metrics with resource attributes

[ChrsMark]

At the moment most of the K8s metrics do not define attributes.

We should have recommendations/requirements on what resources metrics can/must associate with, e.g. k8s.pod, k8s.node etc.

Originally posted by @jsuereth in https://github.com/open-telemetry/semantic-conventions/pull/1406#pullrequestreview-2315786748

[lmolkova]

Related: https://github.com/open-telemetry/semantic-conventions/issues/1276

There is no way to do it in yaml yet and we definitely need it, but it should not block us from documenting resources in markdown as a first step.