[DOCS] Kyuubi internal secure access description

### 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/incubator-kyuubi/issues?q=is%3Aissue) and found no similar issues.

### Which parts of the documentation do you think need improvement?

_No response_

### Affects Version(s)

1.6.0

### Improving the documentation

_No response_

### Anything else

_No response_

### Are you willing to submit PR?

- [ ] Yes I am willing to submit a PR!

The issue names no documentation file, test, or entry point and provides no requested change beyond “internal secure access.” First identify the relevant Kyuubi documentation and clarify the intended description with maintainers; done is a specific documentation target and agreed content to update.

Written by the indexing model from the issue text.