Add multiple user adjustable environments

[Auz]

• Create UI to add environments
• Add backend methods to add/delete/update environments
• Update existing hard coded dev/prod
• Adjust getting started instructions to use environments/api keys
• Automatically add the initial two environments when first starting
• Handle case where api keys are all deleted
• Backwards fill environments for existing users
• Make feature list show toggles for dynamic set of environments (if enabled)
• Adjust UI of feature detail page to handle N environments
• Adjust API endpoint to use dynamic environments

[vercel]

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