docs[minor]: Swap gtag for supabase (#18937)

Added deps:
- `@supabase/supabase-js` - for sending inserts
- `supabase` - dev dep, for generating types via cli
- `dotenv` for loading env vars

Added script:
- `yarn gen` - will auto generate the database schema types using the
supabase CLI. Not necessary for development, but is useful. Requires
authing with the supabase CLI (will error out w/ instructions if you're
not authed).

Added functionality:
- pulls users IP address (using a free endpoint: `https://api.ipify.org`
so we can filter out abuse down the line)

TODO:
- [x] add env vars to vercel

docs/static/js/google_analytics.js

@@ -3,9 +3,3 @@ function gtag(){dataLayer.push(arguments);}
 gtag('js', new Date());
 
 gtag('config', 'G-9B66JQQH2F');
-
-// Only for feedback
-function gtagFeedback(){dataLayer.push(arguments);}
-gtagFeedback('js', new Date());
-
-gtagFeedback('config', 'G-WFT0J048RF');