feat: deploy to gcp via cloudbuild

[jackal998]

All of these configuration files were referenced from those documents/blogs:

• Running Rails on the Cloud Run environment
• Connect to Cloud SQL for PostgreSQL from Cloud Run
• Connect from Cloud Run
• entrypoint file not found
• 如何在幾分鐘內容器化 Rails 專案
• Rails 部署實踐 - 容器化 Rails 專案概述
• Ruby on Rails 容器化最佳指南（一）
• Ruby on Rails 容器化最佳指南（二）