[TASK][MEDIUM] Unlock advanced features of markdown in docs

### What's the level of this task?

MEDIUM

### Code of Conduct

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

### Search before creating

- [X] I have searched in the [task list](https://github.com/orgs/apache/projects/343) and found no similar tasks.

### Mentor

- [X] I have sufficient expertise on this task, and I volunteer to be a mentor of this task to guide contributors through the task.

### Skill requirements

- Sphinx, and maybe some HTML and CSS skills

### Background and Goals

Kyuubi uses Sphinx to build the docs, and `RST` and `Markdown` are mixed-used.

RST is a much more powerful format but easy to mess up and hard to learn, while Markdown is more popular and easy to learn.

Currently, Kyuubi uses a legacy `markdown==3.4.1` for Sphinx markdown support, which lacks some advanced features, e.g. variable substitution, which is likely to be used for "version"

While the recommended powerful markdown solution is `myst_parser` https://www.sphinx-doc.org/en/master/usage/markdown.html, we should investigate and migrate to this one.

### Implementation steps

- configure Sphinx to use `myst_parser`
- make sure everything in docs looks well, especially the configuration page https://kyuubi.readthedocs.io/en/master/configuration/settings.html
- converting at least one RST docs to markdown which has variable substitution

### Additional context

Introduction of [2024H1 Kyuubi Code Contribution Program](https://github.com/apache/kyuubi/issues/6232)

Start by locating Kyuubi's Sphinx configuration and reviewing the configuration settings page, which the issue identifies as needing particular attention. Check how Markdown is currently enabled, investigate myst_parser support and variable substitution, then convert one RST document and verify that the generated documentation still looks correct.

Written by the indexing model from the issue text.