Changes

• Re-oragnize docker folder structure.
• Support Read-only Filesystems by Defaults
  • As a result, envsubst will not run on .env.* files at container startup in production to expand env variables. As an alternative, you can configure PHP Framework to do Environment Variables expanding.
• Upgrade Alpine PHP Image 3.13 -> 3.15
• Upgrade Nginx Version 1.20 -> 1.21