[Docs] Convert rST to MyST (Markdown)

[rafvasq]

This PR migrates the existing documentation from reStructuredText to MyST Markdown, a flavour of Markdown extended for use with Sphinx.

• Add .md template to gitignore
• Upgrade myst-parser to 3.0.1
• Converts .rst docs into .md, preserving content and formatting
• Update filename references to docs from .rst to .md
• In front-end code, update class/function definition references to documentation
  • e.g. :ref: engine_args -> [engine-args](#engine-args)

Closes #10427

[github-actions]

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[mergify]

This pull request has merge conflicts that must be resolved before it can be
merged. Please rebase the PR, @rafvasq.

https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/working-with-forks/syncing-a-fork

[DarkLight1337]

It doesn't look like markdown format works here:

https://vllm--11145.org.readthedocs.build/en/11145/design/multimodal/multimodal_index.html

[rafvasq]

I looked into it, and it turns out that sphinx.ext.autodoc is not compatible with MyST Markdown, but still usable: the simple workaround is that docstrings still use rST. It's working now: https://vllm--11145.org.readthedocs.build/en/11145/design/multimodal/multimodal_index.html#registry.

Longer term, because I think it warrants its own PR, the solution is to use autodoc2 by Sphinx, which supports MyST.

[mergify]

This pull request has merge conflicts that must be resolved before it can be
merged. Please rebase the PR, @rafvasq.

https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/working-with-forks/syncing-a-fork

[DarkLight1337]

I'll take a look at the files one by one this weekend.

Let's try to get this in sometime during the Christmas holidays so we don't get as many merge conflicts 😅

[mergify]

This pull request has merge conflicts that must be resolved before it can be
merged. Please rebase the PR, @rafvasq.

https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/working-with-forks/syncing-a-fork

[youkaichao]

is it possible to keep both rst and myst, so that we can update the doc files one by one in many PRs?

this large PR will easily have conflicts :(

[simon-mo]

i think we should just quickly merge at once, as soon as all the previews are checked for accuracy.

[DarkLight1337]

The link here appears to be broken (that being said, this is also the case on main branch).

[DarkLight1337]

The links for code examples (e.g. https://vllm--11145.org.readthedocs.build/en/11145/getting_started/examples/api_client.html) are also broken.