[CHORE]: Migrate run-gunicorn-v2.sh to run-gunicorn.sh and have a single file (improved startup script with configurable flags)

[crivetimihai]

Title: Enhanced run-gunicorn.sh with process locking, dev mode, and improved production features

Description:

Enhance the run-gunicorn.sh script with several production-ready features and developer conveniences:

New Features:

• Process Lock Protection: Prevents accidental duplicate instances via PID file checking (/tmp/mcpgateway-gunicorn.lock)
• Developer Mode: Hot reload support with GUNICORN_DEV_MODE=true - automatically enables --reload and watches config files
• Application Preloading: Memory optimization with GUNICORN_PRELOAD_APP=true for production deployments
• Auto Worker Detection: Dynamically calculates optimal worker count based on CPU cores (2×CPU+1)
• Database Init Control: Skip DB initialization with SKIP_DB_INIT=true for faster restarts
• Force Start Option: Override lock check with FORCE_START=true when needed

Improvements:

• Added --forwarded-allow-ips="*" for proxy/Kubernetes deployments
• Enhanced error handling with descriptive messages and recovery suggestions
• Proper signal handling and cleanup on exit
• Python 3.x verification to prevent Python 2 usage
• Comprehensive environment variable documentation

Environment Variables:
All existing vars preserved, plus:

• GUNICORN_DEV_MODE - Enable hot reload for development
• GUNICORN_PRELOAD_APP - Preload app for memory savings
• SKIP_DB_INIT - Skip database initialization
• FORCE_START - Force start despite existing instance

This makes the script suitable for both development (with hot reload) and production (with preloading, process protection) while maintaining backward compatibility.