Add utility for lazy model resolution by string label (e.g. "app_label.ModelName")

[Mbulelo_Peyi]

This feature proposes the addition of two utility functions to simplify lazy model resolution in Django:

• get_model_by_label(model_label: str) Resolves and returns a model class from a string label like 'app_label.ModelName'.

• lazy_model(model_label: str) Returns a SimpleLazyObject that lazily resolves a model using the above utility.

These functions are useful when:

• Avoiding circular imports (e.g., in apps.py, signals.py, or settings.py)
• Dynamically referencing models by name
• Loading models safely before the app registry is fully ready

This pattern is currently re-implemented in many Django projects and third-party packages. Including it in Django would standardize a safe, performant, and readable approach to lazy model loading.

The get_model_by_label() function includes:

• Input validation
• Exception handling with ImproperlyConfigured
• Caching via @lru_cache to improve performance