feat(cloudnativePG): support topologySpreadConstraints

A HA `Cluster` is only actually highly available if its instances end up in different failure domains. Pod
anti-affinity alone cannot express that: it only keeps the instances off the same node, not off the same zone,
and `cloudnativePG.affinity` has no way to encode a skew budget. Without `topologySpreadConstraints` a three
instance cluster can legitimately be scheduled into a single availability zone, where a zone outage takes down
the primary and both replicas at once.

Both `affinity` and `topologySpreadConstraints` are rendered only when they are set. The CloudNativePG API
declares them as `omitempty`, so an empty `{}` or `[]` in the manifest would show up as a permanent diff against
the state the operator writes back.

Tolerations deliberately do not get a dedicated value. CloudNativePG has no `spec.tolerations`, it nests them
below `spec.affinity.tolerations`, so they are configured through `cloudnativePG.affinity` like `nodeSelector`
and the anti-affinity settings. A separate top-level value would only have to be folded back into the same place
and would silently conflict with a tolerations list set via `cloudnativePG.affinity`.

Co-authored-by: Copilot <copilot@github.com>

values.yaml

@@ -1178,19 +1178,22 @@ cloudnativePG:
     size: 2Gi
     storageClass: ""
 
-  ## @param cloudnativePG.monitoring.enablePodMonitor Create a `PodMonitor` for the CloudNativePG `Cluster`.
-  monitoring:
-    enablePodMonitor: false
-
-  ## @param cloudnativePG.affinity Affinity for the PostgreSQL pods.
+  ## @param cloudnativePG.affinity Affinity for the PostgreSQL pods. CloudNativePG nests `nodeSelector` and `tolerations` below this key as well.
   affinity: {}
 
   ## @param cloudnativePG.priorityClassName Priority class name for the PostgreSQL pods.
   priorityClassName: ""
 
+  ## @param cloudnativePG.monitoring.enablePodMonitor Create a `PodMonitor` for the CloudNativePG `Cluster`.
+  monitoring:
+    enablePodMonitor: false
+
   ## @param cloudnativePG.resources Kubernetes resources for the PostgreSQL containers.
   resources: {}
 
+  ## @param cloudnativePG.topologySpreadConstraints Topology spread constraints for the PostgreSQL pods.
+  topologySpreadConstraints: []
+
 
 ## @section valkey
 valkey: