Add a migration guide from FastAPI Depends

Docs should cover general tips on how to migrate, replacing fastapi depends with wireup for both functions and class-based dependencies.

```python
@dataclass
class ServiceA:
  service_b: Annotated[ServiceB, Depends(ServiceB)]
  # other dependencies using Depends(...)
```

Then invoked from fastapi: `service_a: Annotated[ServiceA, Depends(ServiceA)]`