feat: add per-namespace webhook support using namespaceSelector and WEBHOOK_PREFIX

[dipensompurasr]

Enhancement description

Add per-namespace webhook support in the cloudnative-pg Helm chart using namespaceSelector and WEBHOOK_PREFIX.

When config.clusterWide=false, the chart should:

• set WEBHOOK_PREFIX to <namespace>- in the operator Deployment
• create prefixed mutating/validating webhook configuration names
• scope webhook entries to the release namespace via namespaceSelector

When config.clusterWide=true, existing cluster-wide behavior must remain unchanged.

Related work

This is the Helm chart companion for operator support tracked in cloudnative-pg/cloudnative-pg#10792.

Scope

• update chart templates for Deployment and webhook configurations
• add chart template tests validating namespace-scoped and cluster-wide rendering