[k8s] define attribute roles for k8s entities

[ChrsMark]

Related to #3002

Changes

This PR defines roles for k8s entities' attributes.

Note: k8s.container and k8s.namespace are left out for now cause they don't define a uid identifying attribute which quite straight-forward to use. They are marked as TODO though for now.

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]
• Links to the prototypes or existing instrumentations (when adding or changing conventions)