Move all contributing docs to this repo

[ptgott]

Instructions for contributing to the documentation and docs engine are distributed between the "Contributing" section of the Teleport docs site and the README of this repo. This change makes this repo the single source of truth for docs contribution guidance.

Moving all docs contribution guidance into this repo has the following advantages:

• It's easier to keep this information up to date.
• We can free up a navigation sidebar section on the main docs site while still keeping this information discoverable.

Summary of changes:

• Move all pages from the /docs/contributing/documentation section of the docs site into the docs-contributors directory of this repo. This required changing UI components in these pages to be compatible with GitHub Markdown.
• Organize yarn information into a command reference and move the reference into docs-contributors.
• Remove README info that overlaps with the UI reference.
• Move docs site configuration information from the README into a separeate guide.
• Remove instructions for running a dev server with Docker. These have often been a source of confusion for readers, and require the same initial setup as using yarn.

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Name	Status	Preview	Comments	Updated (UTC)
docs	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Feb 8, 2024 5:35pm

[ptgott]

Reviewer note: once this is merged, I'll remove the "Contributing" section from the Teleport docs site.