Add official Helm chart for Karapace Schema Registry

# What is currently missing?

There is currently no official Helm chart for deploying Karapace Schema Registry.

This forces users to maintain custom Kubernetes manifests or private Helm charts. An official chart would simplify installation, upgrades, and standardize Kubernetes deployments.

# How could this be improved?

Add an official Helm chart including:

- Deployment/StatefulSet
- Service (optional Ingress)
- Configurable values.yaml (Kafka, Schema Registry settings, resources, replicas)
- Liveness/readiness probes
- Support for Secrets/ConfigMaps

Basic documentation and example values would also be helpful.

# Is this a feature you would work on yourself?

* [x] I plan to open a pull request for this feature