[FEATURE] Add Docker Setup and Documentation

[pulk17]

Please prefix your pull request with one of the following: [FEATURE] [FIX] [IMPROVEMENT].

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This PR introduces a complete Docker-based development environment for the Sample Platform. It allows developers to spin up the entire application stack (Flask + MySQL) with a single command, eliminating manual dependency installation and configuration headaches.

Key Features

• One-Command Setup: docker compose up --build handles everything from database creation to dependency installation.
• Live Code Reloading: The local source code is mounted into the container, so changes are reflected immediately without rebuilding.
• Automated Database Management:
  • Automatically waits for MySQL to be healthy.
  • Handles schema creation and migration stamping (flask db stamp head) on the first run.
  • Seeds the database with an admin user and sample data (configurable via .env).
• Google Cloud Storage (GCS) Emulation:
  • Automatically generates a dummy service-account.json if one is missing, preventing startup crashes.
  • Supports mounting a real GCS bucket via gcsfuse if credentials are provided.
• Security Best Practices:
  • SECRET_KEY and CSRF_SESSION_KEY are generated at runtime.
  • Runs with a non-root user (Gunicorn).

File Overview

• Dockerfile: Multi-stage build based on Python 3.11-slim.
• docker-compose.yml: Orchestrates the Flask backend and MySQL 8.0 database.
• docker-entrypoint.sh: A robust startup script that handles:
  • Secret key generation.
  • Git repository initialization (required for build commit display).
  • Database waiting and migration strategies.
  • Gunicorn execution.
• DOCKER.md: Comprehensive documentation on usage, architecture, and troubleshooting.
• env.example: A template for environment variables tailored for Docker.
• .dockerignore: Optimizes build context by excluding unnecessary files.

Design Decisions & Trade-offs

• Runtime Secrets: We generate secrets in the entrypoint instead of the Dockerfile to prevent leaking them in image layers and to ensure every container has unique keys.
• GCS Mounting: We mount GCS buckets to /mnt/gcs_repository instead of directly to /repository to avoid conflicts with Docker's volume mounting behavior.
• Database Stamping: On a fresh DB, we use flask db stamp head because create_all() builds the schema faster than running 50+ migrations sequentially.

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Documentation: See DOCKER.md for full details.

[sonarqubecloud]

Quality Gate failed

Failed conditions
C Reliability Rating on New Code (required ≥ A)

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