add k8s.container.status.state and k8s.container.status.reason metrics

[povilasv]

Fixes https://github.com/open-telemetry/semantic-conventions/issues/1672

Changes

Adds k8s.container.status.state metric, it would allow us to alert and monitor containers in not ready state.

I'm still not sure if this should be multiple different metrics or a single one :thinking:

The current problems, with single metric:

• Running state doesn't have a reason, so we would set reason to empty.
• Waiting state and Terminated state have different sets of reasons:

Waiting state - "ContainerCreating", "CrashLoopBackOff", "CreateContainerConfigError", "ErrImagePull", "ImagePullBackOff"

Terminated state - "OOMKilled", "Completed", "Error", "ContainerCannotRun"

Alternative approach would be to do what KSM does:

• k8s.container.status.state metric without reason attribute.
• k8s.container.status.waiting_reason metric for waiting reason enum.
• k8s.container.status.terminated_reason metric for terminated reason enum.

This is not intended to merge, I would appreciate any feedback to see what we want to do here.

Merge requirement checklist

• [ ] CONTRIBUTING.md guidelines followed.
• [ ] Change log entry added, according to the guidelines in When to add a changelog entry.
  • If your PR does not need a change log, start the PR title with [chore]
• [ ] schema-next.yaml updated with changes to existing conventions.