Markdown repairs & re-enable smart markdown docs in Playbook

[jasoncypret]

What does this PR do? A clear and concise description with your runway ticket url.

• ✅ enables .md extension in rails
• ✅ enables renderof markdown as partials
• ✅ Custom HTML blocks for Tables, & Headings
• ✅ Updated markdown styling based on new editor
• ✅ Adds dynamically rendered markdown as a template through routes
• ✅ Adds dynamically generated markdown title
• ✅ Adds dynamically generated "edit this" button
• ✅ Removed SLIM dependency
• ✅ Dynamically generated docs navigation based on docs folder structure
• ✅ Upgrades Redcarpet 3.5 -> 3.6

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• LABELS Add a label: enhancement, bug, improvement, new kit, deprecated, or breaking. See Changelog & Labels for details.
• DEPLOY I have added the milano label to show I'm ready for a review.
• TESTS I have added test coverage to my code.