Create staging environment

[0ptim]

• [x] Create new project in Supabase JellyChat-Staging
• [x] Create organization and app on fly.io jellychat-staging
• [x] Check if all GitHub actions deployments work (PR and merge) and if staging and production environments are correctly built/deployed.
• [x] Create overview on what secrets/variables are on which platform and which environment, so it's clear which points to which.

Staging

• https://fly.io/apps/jellychat-staging
  • https://jellychat-staging.fly.dev/
• https://supabase.com/dashboard/project/iajfqvpslzrtmvekqwpv

Production

• https://fly.io/apps/jellychat
  • https://jellychat.fly.dev/
• https://supabase.com/dashboard/project/cofmxsabxteiidryklyg