Not a direct, safe, web-based link that works instantly. But the functional equivalent exists:
While some earlier Hitman titles had built-in console commands to unlock levels, Absolution is more restrictive. There is no official "unlock all levels" cheat code; however, you can use trainers from platforms like WeMod to enable "God Mode" or "Unlimited Instinct," making it much faster to blaze through missions yourself to unlock them. Mission List for Reference
The level editor allows you to create your own custom missions. Here's how to access them: