WIP - docs style

[jeff-bruemmer]

WIP
https://app.notion.com/p/metabase/Docs-metempsychosis-3f469354c901808fa605c050b88f7327?source=copy_link

Adds:

• Tabbed navigation (we'll want to update the nav content following this merge)
• Dark mode
• Click to copy markdown pages (along with .md pages for supported mb versions---should we do all versions?) llm.txt now links to these pages (instead of github raw; bc image links + includes).

Removes:

• Top marketing nav

Improves:

• Line breaks
• Table layout/design. Major improvements for embedding docs, and necessary to unblock wide tables like db feature support: docs - db feature support metabase#83996
• Paragraph width
• Nav placement
• And more!

Excessive detail:

• Only NewDocsLayout pages and the docs 404 get the new header and theme.
• Sidebar shows only the active category with all groups expanded; opening one group no longer collapses the others
• docs home loses breadcrumbs and the feedback widget
• Version picker, search and What's new move from the top bar into the header
• Search remembers Search vs Ask.

[bpander]

Closing since we've folded the docs repo into the www monorepo so we're archiving this repo. This branch was ported over to that repo: https://github.com/metabase/metabase.github.io/pull/6683.