[telemetry] Define lifecycle and stability of telemetry

[mx-psi]

On the GA Roadmap, we have

• Metrics, or a subset of them, should be marked as stable in the documentation
• [...]
• Stability expectations and lifecycle for telemetry should be documented, so that users can know what they can rely on for their dashboards and alerts

A starting point can be https://kubernetes.io/docs/concepts/cluster-administration/system-metrics/#metric-lifecycle

[lavishpal]

@mx-psi Could you assign this issue to me and it will be helpful if you provide guidance on how to get started?

[mx-psi]

@lavishpal We can start with a document that lists out what we guarantee from a stable metric (in terms of what can change). We can initially host the document in the docs/ folder of this repository. Once we have that, we can consider next steps