[FEATURE] Allow passing `self` to steps created with `step` decorator

**Is your feature request related to a problem? Please describe.**
`process` function created with `step` decorator doesn't have a way to access `Step` class attributes.

**Describe the solution you'd like**

```python
from distilabel.step import step

@step(step_type="generator", pass_self=True)
def MyGenerator(self, offset: int = 0): ...
```