Add an Observability Compatibility Policy

docs/monitoring-guidelines.md‎

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+## Cluster Network Addons Operator Monitoring
+
+### Observability Compatibility Policy
+
+This policy covers all Cluster Network Addons Operator observability signals. Like: metrics (and their names, label sets, and types), Prometheus recording rules, and alerting rules. Unless explicitly stated otherwise, these signals are considered implementation details and are subject to change.
+
+- Stability: Cluster Network Addons Operator does not guarantee long-term backwards compatibility for observability signals. Names, labels, types, and semantics may change between releases to improve correctness, performance, or operability.
+- Deprecation: When feasible, we will deprecate renamed or removed signals by:
+  - Marking the old name as Deprecated in documentation.
+  - Optionally providing short-lived compatibility recording rules (aliases) that map new signals to old names.
+  - Keeping deprecated signals for at least one minor release when possible. In exceptional cases (security, correctness, or scalability), changes may occur without a deprecation window.
+- Communication: Material changes will be documented in release notes and reflected in `docs/observability/metrics.md`. Alert and rule updates will also be surfaced via PR descriptions.
+- Consumer guidance: Dashboards and alerts should:
+  - When creating PromQL queries, expect label sets to change; avoid relying on exhaustive or fixed labels. Select, join, and group by the minimum labels required.
+    - Example: Prefer `sum by (namespace)(...)` over `sum by (namespace,pod,container,instance)(...)` when possible.
+  - Treat deprecated signals as temporary and migrate to replacements promptly.
+
+Contributors adding or changing observability signals should update documentation, consider temporary compatibility rules if practical, and include migration notes in the PR and release notes.