Support a dedicated PVC for logs (separate from pgData)

Proposal

K8SPG-851 (and the shared tech design in K8SPXC-485 / K8SPSMDB-297) adds persistent logging so logs survive a Pod restart, but in the current implementation logs are written to the same PVC as the instance data (e.g. pgBackRest logs to the pgData volume). There's no option to give logs their own PVC.

Add an optional dedicated logs volume claim spec, following the same pattern already used for WAL
a new LogVolumeClaimSpec that, when set, mounts a separate PVC for Patroni/Postgres/pgBackRest logs instead of writing them to pgData. When unset, behavior is unchanged.

Use-Case

1. As a user, I don't want runaway log growth to risk filling my Postgres data volume and causing an outage.
2. As a user, I want to choose a cheaper/different storage class for logs than for my Postgres data.
3. As a user, I want log volume size to scale independently of data volume size.

Is this a feature you are interested in implementing yourself?

Yes

Anything else?

No response

Start by tracing the existing WAL volume-claim specification and its PVC and mount wiring. Compare how Patroni, Postgres, and pgBackRest logs currently use pgData, then define the done state as an optional LogVolumeClaimSpec that mounts a separate logs PVC while preserving current behavior when it is unset.