Feature: Add support for multiple docsets and MI3XX reference design breakout

[mbenavidez-amd]

Motivation

This pull request introduces a new unified documentation build system for the monorepo, improves image rendering in dark and light modes, and updates the organization and content of the cluster design reference materials. It also adds a dedicated Read the Docs configuration for the MI3XX reference docset and makes minor content and configuration cleanups.

Technical Details

Documentation build system:

• Added build_docs.py, a script that automatically discovers and builds all Sphinx docsets in the repo, supporting per-docset builds, cleaning, and integration with VS Code and CI.

Read the Docs configuration:

• Added a dedicated .readthedocs.yaml for the MI3XX reference docset with a monorepo-aware build guard.
• Removed PDF output from the main docset's Read the Docs config to simplify formats. Also redundant with the recent per-page PDF configurations.

Styling improvements:

• Improved image rendering in both dark and light modes by adjusting background and brightness for images and customizing error tables for troubleshooting pages in both docs/_static/css/custom.css and reference-architecture/MI3XX/_static/css/custom.css.

Content and navigation updates:

• Moved cluster architecture and network design materials to an external reference page, updating cluster-design.rst accordingly.
• Cleaned up and reformatted the main documentation index and navigation files for clarity and consistency.

These changes streamline the documentation workflow, improve the user experience for both readers and contributors, and clarify the organization of reference materials.

Test Plan

Sucessfully build and test documentaiton locally.

Test Result

Local build was successful.

Submission Checklist

• Look over the contributing guidelines at https://github.com/ROCm/ROCm/blob/develop/CONTRIBUTING.md#pull-requests.