dbaas: bump pg_cluster trigger so the checkpoint/WAL params actually apply

a2c8f906 added checkpoint_timeout=15min + max/min_wal_size to the CNPG
Cluster YAML, but the cluster is applied via null_resource.pg_cluster +
local-exec kubectl apply, which only re-runs when its `triggers` change.
The YAML edit didn't bump a trigger, so the change was inert and never
applied (incl. via CI). Bump the pg_params trigger so the kubectl apply
re-runs and CNPG hot-reloads the new params (reloadable, no restart).

Landing it via a targeted apply (-target=null_resource.pg_cluster) to avoid
3 pre-existing unrelated drifts in this stack -- notably a mysql_standalone
volumeClaimTemplate annotation diff the apiserver rejects as immutable,
which is what fails broad dbaas applies (and silently blocked a2c8f906).

Refs: code-oflt.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

stacks/dbaas/modules/dbaas/main.tf

@@ -1113,7 +1113,7 @@ resource "null_resource" "pg_cluster" {
     storage_size  = "20Gi"
     storage_class = "proxmox-lvm-encrypted"
     memory_limit  = "3Gi"
-    pg_params     = "v3-shared1024-walcomp-workmem16-max200"
+    pg_params     = "v4-shared1024-walcomp-workmem16-max200-ckpt15m-wal4g-minwal1g"
     affinity      = "required-hostname-v1"
   }