fix: target namespace of grafana secrets

[merll]

📌 Summary

This is a followup of moving platform secrets from values to SealedSecret resources. These corrects the target namespace needed by the platform Grafana instance.

🔍 Reviewer Notes

Grafana currently fails to start in main. With this change, pods should be configured correctly.

🧹 Checklist

• Code is readable, maintainable, and robust.
• Unit tests added/updated

[svcAPLBot]

Comparison of Helm chart templating output:

# raw/templates/resources.yaml

@@ metadata.namespace @@
# external-secrets.io/v1/ExternalSecret/grafana/grafana-loki-datasource-secret
! ± value change
- monitoring
+ grafana

@@ metadata.namespace @@
# external-secrets.io/v1/ExternalSecret/grafana/grafana-oidc-secret
! ± value change
- monitoring
+ grafana

@@ metadata.namespace @@
# external-secrets.io/v1/ExternalSecret/grafana/grafana-admin-secret
! ± value change
- monitoring
+ grafana

# rabbitmq-cluster-operator/templates/messaging-topology-operator/validating-webhook-configuration.yaml

# values-repo.yaml