build: add nixpacks.toml base on Dockerfile

[Rot4tion]

Add nixpacks.toml based on Dockerfile

What?

Added a nixpacks.toml configuration file that replicates the build and deployment process defined in the existing Dockerfile, providing an alternative deployment method for the PayloadCMS application.

Why?

• Enables deployment on platforms that support Nixpacks (like Railway, Render, etc.)
• Simplifies the deployment configuration with a more concise format
• Maintains the same build and runtime behavior as the Docker setup
• Provides flexibility for different deployment environments

How?

• Created a nixpacks.toml file that follows the same build phases as the Dockerfile:
  • Install dependencies using pnpm
  • Build the application
  • Prepare the output by copying necessary files
• Configured environment variables for production
• Set up caching for node_modules and pnpm store to improve build performance
• Defined the start command to run the Next.js server

This configuration maintains compatibility with the existing Docker-based deployment while offering an alternative deployment method.