feat: add ALB+Cognito authentication and security enhancements

[marcio-rg]

• Add optional ALB+Cognito authentication with enable_authentication flag
• Implement IP-based access restrictions via allowed_ips parameter
• Add SSL/TLS support with ACM certificate integration
• Create Cognito user pool and user pool client for authentication
• Add create-user.sh script for easy user management
• Update ECS task definition with authentication environment variables
• Enhance documentation with security configuration examples
• Add terraform.tfvars.example template for easy setup
• Update UI styling and templates for authentication flow
• Add S3 bucket policy and ALB access logging configuration

TODO

• Updated architecture documentation (diagram)
• Update UI screenshot with example of logged-in screen.

Testing

• Tested with authentication disabled (default behavior)
• Tested with authentication enabled
• Verified IP restrictions work correctly
• Confirmed SSL/TLS integration

Key Features Added

• Optional ALB+Cognito Authentication: Controlled via `enable_authentication` flag
• IP-based Access Control: Restrict access via `allowed_ips` parameter
• SSL/TLS Support: Integration with ACM certificates for HTTPS
• User Management: Convenient `create-user.sh` script for Cognito user creation
• Enhanced Security: Proper authentication flow with session management

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