[CT-876] Github Actions - Check Markdown Links

[jiajames]

• Add markdown-link-check to crawl through .md/.mdx files and run links
  • Added some ignores/etc. in mlc_config.json for where it didn't work well
• Removed slate github actions for now
• Fixed up all links!

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Name	Status	Preview	Comments	Updated (UTC)
v4-teacher	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	May 30, 2024 4:30pm

[linear[bot]]

CT-876 Implement Github Actions to auto catch issues