feat: add Docker registry authentication support

[shyim]

Summary

This PR adds comprehensive Docker registry authentication support to testcontainers-php, allowing users to pull private images from registries like GitHub Container Registry, Docker Hub, and custom registries.

Changes

• Added DockerAuthConfig class to handle authentication configuration
• Support for DOCKER_AUTH_CONFIG environment variable
• Support for reading from ~/.docker/config.json
• Support for credential stores (osxkeychain, wincred, pass, etc.)
• Automatic registry detection from image names
• Updated pullImage() method to use authentication when available
• Added comprehensive unit tests

Motivation

Currently, when pulling private Docker images, authentication must be hardcoded in the pullImage() method. This PR implements the same authentication mechanisms as the Docker CLI, making it seamless for users to work with private registries.

Usage Examples

Using DOCKER_AUTH_CONFIG environment variable

export DOCKER_AUTH_CONFIG='{
  "auths": {
    "ghcr.io": {
      "username": "username",
      "password": "pat_token"
    }
  }
}'

Using Docker config file

The library will automatically read from ~/.docker/config.json if DOCKER_AUTH_CONFIG is not set.

Using credential stores

{
  "auths": {
    "ghcr.io": {}
  },
  "credsStore": "osxkeychain"
}

Test plan

• Unit tests for all authentication methods
• PHPStan validation passes
• Manual testing with private registries
• CI/CD validation

🤖 Generated with Claude Code

[shyim]

I wanted to try out AI to get #34 fixed.
I will review later the changes 😅

[jorgsowa]

This PR works nicely with private registries 👍🏽