:memo: Fix/Add High Availability documentation for Kubernetes and etcd

### Code of Conduct

- [X] I agree to follow this project's [Code of Conduct](https://www.apache.org/foundation/policies/conduct)

### Search before asking

- [X] I have searched in the [issues](https://github.com/apache/kyuubi/issues?q=is%3Aissue) and found no similar issues.

### What type of changes will we make to the documentation?

Usage of New Feature

### Affects Version(s)

master

### Improving the documentation

I was looking into how to deploy Kyuubi with HA via helm chart and on the surface it looks like the solution is to deploy zookeeper and configure that. Upon further digging, I found options for etcd and work such as #1392 that seems to indicate that HA is possible via etcd in a Kubernetes deployment. It seems the documentation is not up to date with the abilities the Kyuubi provides. I don't know what would be required to support HA in Kubernetes as the deployment has 2 replicas, but I don't see anything in the configmap to indicate HA. Is Kyuubi coordinating this itself somehow or would one need to point Kyuubi to either the k8s etcd or an external cluster similar to a zookeeper setup?

### Are you willing to submit PR?

- [X] Yes. I would be willing to submit a PR with guidance from the Kyuubi community to improve.
- [ ] No. I cannot submit a PR at this time.

Start by reviewing the Kubernetes Helm chart, its ConfigMap, and the existing etcd and ZooKeeper deployment documentation. Determine which HA configurations and replica behavior Kyuubi supports, then document the required Kubernetes and external-cluster settings and explain what a complete HA deployment should look like.

Written by the indexing model from the issue text.