Add default values to prompts and reorganize admin setup

• Add default values to all yes/no prompts for unattended installations
• Move admin email input to domain configuration section
• Use admin email as default for SSL certificate notifications
• Reorganize admin account setup section (removed duplicate prompt)
• Move demo credentials removal before yarn build step
• Simplify demo removal by using sed instead of awk
• Comment out SESSION_DOMAIN in .env.example instead of empty