## Description
Currently, the docs page has the home book opened by default. This PR
updates the .ts so that the sidebar books are collapsed when you first
open the webpage
# What does this PR do?
First step towards cleaning up the API reference section of the docs.
- Separates API reference into 3 sections: stable (`v1`), experimental (`v1alpha` and `v1beta`), and deprecated (`deprecated=True`)
- Each section is accessible via the dropdown menu and `docs/api-overview`
<img width="1237" height="321" alt="Screenshot 2025-09-30 at 5 47 30 PM" src="https://github.com/user-attachments/assets/fe0e498c-b066-46ed-a48e-4739d3b6724c" />
<img width="860" height="510" alt="Screenshot 2025-09-30 at 5 47 49 PM" src="https://github.com/user-attachments/assets/a92a8d8c-94bf-42d5-9f5b-b47bb2b14f9c" />
- Deprecated APIs: Added styling to the sidebar, and a notice on the endpoint pages
<img width="867" height="428" alt="Screenshot 2025-09-30 at 5 47 43 PM" src="https://github.com/user-attachments/assets/9e6e050d-c782-461b-8084-5ff6496d7bd9" />
Closes#3628
TODO in follow-up PRs:
- Add the ability to annotate API groups with supplementary content (so we can have longer descriptions of complex APIs like Responses)
- Clean up docstrings to show API endpoints (or short semantic titles) in the sidebar
## Test Plan
- Local testing
- Made sure API conformance test still passes
# What does this PR do?
- Docusaurus server setup
- Deprecates Sphinx build pipeline
- Deprecates remaining references to Readthedocs
- MDX compile errors and broken links to be addressed in follow-up PRs
<!-- Provide a short summary of what this PR does and why. Link to relevant issues if applicable. -->
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## Test Plan
```
npm install
npm gen-api-docs all
npm run build
```
<!-- Describe the tests you ran to verify your changes with result summaries. *Provide clear instructions so the plan can be easily re-executed.* -->
