:memo: Consolidate a documentation format to a single approach

### 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?

Refactoring

### Affects Version(s)

master/1.11

### Improving the documentation

### **Description**
Currently, the Apache Kyuubi documentation uses a hybrid approach, mixing **reStructuredText (.rst)** and **Markdown (.md)** files, while being processed by **Sphinx**.

While this hybrid approach provides flexibility (using `myst-parser` for Markdown), it introduces several challenges:
1. Contributors need to be familiar with both syntaxes.
2. Cross-referencing between RST and MD files can be error-prone and hard to detect.
3. The build pipeline relies on multiple Sphinx extensions (like `myst-parser`, `sphinx-markdown-tables`) to bridge the gap.
4. Formatting features available in RST might not be easily replicable in Markdown (or vice-versa).

**I propose migrating to a single technology to streamline the contribution process and improve documentation quality.**

---

### **Technology Comparison**

Below is an analysis of the two primary paths for consolidation:

#### **Option 1: Migrate to Markdown (using MyST-Parser)**
* **Pros:**
* Markdown is the de facto standard for most developers, so it is easier for new contributors.
* Better preview support in GitHub, IDEs, and other tools.
* MyST (Markedly Structured Text) provides almost all the power of RST (directives, roles) while remaining valid Markdown.
* **Cons:**
* Once we start using advanced features, the Markdown "cleanliness" can get cluttered with curly braces and colons.
* Some advanced Sphinx features or specialized extensions may still favor RST's native structure.

#### **Option 2: Migrate to reStructuredText (RST)**
* **Pros:**
* RST is the native format for Sphinx, offering the most robust support for technical documentation features.
* Eliminates the need for "bridge" plugins like `myst-parser`.
* **Cons:**
* RST syntax is more verbose and less intuitive for casual contributors compared to Markdown.
* Limited rendering outside of Sphinx-based environments.

---

### **Action Plan**
1. Decide on the target format (Markdown/MyST vs. RST).
2. Convert a few effortless directories to the target format using automated tools or AI agents to verify the approach.
3. Deprecate a non-target format in contributing guidelines.
4. Convert other pages, including those requiring fixing broken cross-references and formatting edge cases.
5. Remove unnecessary Sphinx dependencies from `docs/requirements.txt` and configuration from `conf.py` after migration.

---
**What do you think?** Should we standardize on Markdown for ease of contribution or stick with RST for its native power?

### 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.