fix: Dockerize improvements - add missing build args and Docker instructions

[fityannugroho]

PR Checklist

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• The commit message follows our Contributing Guidelines
• Tests for the changes have been added (optional, for bug fixes or features)
• Docs have been added / updated (optional, for bug fixes or features)

PR Type

What kind of change does this PR introduce?

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• Bug fix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Documentation improvements

What is the current behavior?

Please describe the current behavior that you are modifying, or link to a relevant issue.

Issue Number: N/A

The current Docker setup has several issues:

1. Missing DB_PROVIDER build argument in docker-compose.yml, which causes build failures when the Dockerfile expects this argument
2. Lack of comprehensive Docker instructions and patterns for developers working with containerization
3. No clear guidance on Docker-related development workflows and common troubleshooting

What is the new behavior?

This PR fixes the Docker configuration and adds comprehensive documentation:

1. Fixed docker-compose.yml: Added missing DB_PROVIDER build argument to ensure proper Docker builds
2. Added Docker instructions: Created .github/instructions/docker.instructions.md with:
   • Docker patterns and best practices for the idn-area API
   • Key commands for development and deployment
   • Database connection strategies (containerized vs host-based)
   • Common troubleshooting tips for Docker-related issues
   • E2E testing strategies with containerized databases

The changes ensure that Docker builds work correctly and provide clear guidance for developers on Docker usage patterns.

Other information

Changes made:

• docker-compose.yml: Added DB_PROVIDER build arg to fix build failures
• .github/instructions/docker.instructions.md: New comprehensive Docker documentation covering:
  • Production image patterns with multi-stage builds
  • Testing strategies (host-based E2E with containerized DB)
  • Database connection patterns
  • Key commands for development workflow
  • Common issues and solutions

These improvements align with the project's instruction-based development approach and ensure smooth Docker-based development experience.