Refactor: remove developer settings / custom infra api domain

[ben-fornefeld]

• adds a new required env variable INFRA_API_URL
• removes outdated required env variable NEXT_PUBLIC_DEFAULT_INFRA_DOMAIN
• refactors the infra api calls to use the new env variable
• refactors/cleans up server utils
• removes cookie encryption because this was only used on the developer settings
• removes the developer settings dialog
• removes the developer settings route for settings the api url cookie
• refactor README.md & .env.example

additionally

• requires necessary KV envs for @vercel/kv package to work correctly in middleware

[linear]

E2B-2431 Remove "Developer Settings"

[vercel]

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[dobrac]

lgtm