I notice there's a mismatch between your request and the provided PR content. You've asked me to generate reference documentation for "new or changed SQL statements," but PR #167902 doesn't introduce any SQL statements.

This PR adds certificate lifecycle metrics to help operators monitor certificate rotation and expiration. The changes are:

1. New metrics families:

   • security.certificate.last_rotation.* - Unix timestamps of last certificate rotations
   • security.certificate.expiry_days.* - Days until certificate expiration

2. Affected certificate types: ca, client-ca, ui-ca, ca-client-tenant, node, node-client, ui, client-tenant

3. Implementation details: Added to certificate_manager.go and certificate_metrics.go

Since this is about monitoring metrics rather than SQL statements, would you like me to:

1. Generate metrics documentation (explaining how to use these new certificate monitoring metrics)
2. Wait for a different PR that actually contains SQL statement changes
3. Clarify what type of documentation you need for this specific PR

The metrics would typically be accessed through system tables like crdb_internal.node_metrics or exported via Prometheus, but the PR itself doesn't introduce new SQL syntax.

Which direction would you prefer?