fix(chart): webhook cert SAN must use .Release.Namespace, not .Values.service.namespace

[grkml]

Description

The redis-operator chart builds the cert-manager Certificate dnsNames from .Values.service.namespace (default redis-operator), but the webhook Service and the MutatingWebhookConfiguration clientConfig both use .Release.Namespace:

Template	Namespace source	Resolves to (release ns = ot-operators)
templates/cert-manager.yaml (Certificate SAN)	.Values.service.namespace	webhook-service.redis-operator.svc
templates/service.yaml (Service)	.Release.Namespace	webhook-service.ot-operators.svc
templates/mutating-webhook-configuration.yaml (clientConfig)	.Release.Namespace	webhook-service.ot-operators.svc

When the chart is installed into any namespace other than the service.namespace default, the Certificate SAN no longer matches the DNS name the API server actually dials, so the webhook TLS handshake fails the SAN check. Because the mutating webhook is failurePolicy: Fail, this is silent at install time and only surfaces as a 503 (x509/SAN error) on the first Redis CR admission.

This PR pins the SAN to .Release.Namespace so it always matches the Service the webhook is reached at.

Reproduction

```console
$ helm template redis-operator charts/redis-operator -n ot-operators
--set redisOperator.webhook=true --set certmanager.enabled=true
```

Before — Certificate SAN vs. webhook Service disagree:
```yaml

Certificate

dnsNames:

• webhook-service.redis-operator.svc # .Values.service.namespace

MutatingWebhookConfiguration -> clientConfig.service

name: webhook-service
namespace: ot-operators # .Release.Namespace
```

After this change — they match:
```yaml
dnsNames:

• webhook-service.ot-operators.svc
• webhook-service.ot-operators.svc.cluster.local
  ```

Type of change

• Bug fix (non-breaking change which fixes an issue)

Checklist

• Functionality/bugs have been confirmed to be unchanged or fixed (verified via helm template into a non-default namespace).
• I have performed a self-review of my own code.
• Tests have been added/modified and all tests pass. (chart template change; no unit tests exist for the cert template — happy to add a helm unittest case if the maintainers want one.)
• Documentation updated where necessary.

Additional Context

After this change .Values.service.namespace is no longer referenced by any template. I left the value in place to keep this a minimal, non-breaking fix — glad to remove it (and the README row) in a follow-up if you'd prefer.

[iamabhishek-dubey]

Please work on DCO check for commit sign off