repo_manager domain with security hardening, improved configuration management

[snarthan]

This PR implements major modernization improvements for the repo_manager domain, focusing on security hardening, configuration management, and code quality
enhancements.

Key Changes

Security Enhancements

• Add comprehensive security documentation (docs/security.md)
• Implement no_log for all credential operations to prevent exposure
• Enable ansible-lint security rules (no-log-password, risky-file-permissions)
• Mask passwords in deployment configuration debug output
• Add credential logging protection across all modules

Configuration Management

• Replace hardcoded /opt/omnia paths with environment variable references (OMNIA_DATA_PATH)
• Add environment variable support for portability
• Update container sync policy configuration
• Refactor RPM repository processing configuration with new timeout and parallelism settings
• Add thread pool size configuration with environment variable override support

Code Quality & Validation

• Add comprehensive CHANGELOG.md following Keep a Changelog format
• Add code validation script (scripts/validate_code.sh) with ansible-lint, bandit, and syntax checks
• Remove obsolete software-specific validation logic
• Simplify validation error messages and improve clarity
• Fix Jinja2 template syntax errors in credential handling

Architecture Improvements

• Add new utility modules (repo_logger.py, repo_processor.py, tag_validator.py)
• Improve error handling and logging infrastructure
• Refactor credential collection with comprehensive role metadata
• Add Pulp health check functionality
• Update input validation schema and validators

Documentation

• Add domain-level security documentation with SSL/TLS considerations
• Document credential management best practices
• Add input validation and security hardening guidelines

Configuration Changes

• Update default parallel execution settings (default_nthreads: 1)
• Add container sync policy configuration (immediate for airgap)
• Refactor pulp_config deprecation and migration to rpm_repo_config
• Add comprehensive timeout and stuck detection configuration