Add DuckLake with MinIO object storage support

[EDsCODE]

Summary

• Add docker-compose.yaml with PostgreSQL (metadata catalog) and MinIO (S3-compatible object storage)
• Add S3 credential configuration with two providers:
  • config: explicit credentials for MinIO or access keys
  • credential_chain: AWS SDK chain (env, config, sts, sso, instance, process)
• Add scripts/seed_ducklake.sh to populate DuckLake catalog with sample e-commerce/analytics data
• Add duckgres.yaml pre-configured for local Docker setup
• Update README with setup instructions and configuration documentation

New Configuration Options

ducklake:
  metadata_store: "postgres:..."
  object_store: "s3://bucket/path/"
  s3_provider: "config"           # or "credential_chain"
  s3_endpoint: "localhost:9000"   # for MinIO
  s3_access_key: "..."
  s3_secret_key: "..."
  s3_region: "us-east-1"
  s3_use_ssl: false
  s3_url_style: "path"            # or "vhost"
  s3_chain: "env;config"          # for credential_chain
  s3_profile: "my-profile"        # for credential_chain

Test plan

• Run docker compose up -d to start PostgreSQL and MinIO
• Run ./duckgres --config duckgres.yaml to start server
• Run ./scripts/seed_ducklake.sh to seed sample data
• Verify data in MinIO console at http://localhost:9001
• Query tables via psql: SELECT * FROM ducklake.main.products LIMIT 5;

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