feat: Add namespace suffix to webhooks

[maxlengdell]

When deploying multiple CloudNativePG operators in single-namespace mode on the same cluster, the
MutatingWebhookConfiguration and ValidatingWebhookConfiguration resources collide because they use hardcoded names
(cnpg-mutating-webhook-configuration and cnpg-validating-webhook-configuration). This makes it impossible to run
isolated operator instances per team/namespace without webhook conflicts.

Add a config.namespacedWebhooks Helm value (default false) that, when set to true:

1. Appends - to the webhook configuration resource names (e.g.
   cnpg-mutating-webhook-configuration-cnpg-team-a)
2. Sets the ENABLE_WEBHOOK_NAMESPACE_SUFFIX environment variable on the operator deployment so it can locate its own
   webhook configurations at runtime
3. Adds a namespaceSelector with kubernetes.io/metadata.name: to each webhook entry, ensuring each
   operator's webhooks only intercept resources in its own namespace

Alternatives that have been considered:

• Using fullnameOverride to differentiate releases — this doesn't help because webhook configuration names are
  hardcoded independently of the Helm release name.
• Manually patching webhook names post-install — fragile and breaks on upgrades.
• Disabling webhooks entirely for some instances — loses admission validation.

Additional context

This corresponds to the operator-side change in cloudnative-pg/cloudnative-pg#10420 that introduces the
ENABLE_WEBHOOK_NAMESPACE_SUFFIX configuration parameter. The ClusterRole and ClusterRoleBinding already use {{ include
"cloudnative-pg.fullname" . }} and are unique per release, so they don't require changes.