Feature Aptfile Dependencies

[viktorianer]

Motivation / Background

This PR introduces a new DevContainer feature, Aptfile Dependencies, that simplifies managing apt package installations in development environments. Inspired by [heroku-buildpack-apt](https://github.com/heroku/heroku-buildpack-apt), it allows developers to specify system dependencies in an Aptfile.dev file, automating their installation during container setup.

This change is required to streamline and standardize the process of handling apt dependencies in DevContainers, reducing manual configuration and potential errors.

Example Aptfile.dev usage:

# Video processing
ffmpeg
libvips

# PDF utilities
poppler-utils

# Database libraries
libpq-dev

Example configuration in devcontainer.json:

"features": {
    "ghcr.io/viktorianer/devcontainer-features/apt:1": {
        "devFile": "Aptfile.dev"
    }
}

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Development Checklist

• Add and run tests
• Add and run global test
• Update README
• Update documentation for developers
• Check best practices