Add `target` parameter to `pipe_input`

**Is your feature request related to a problem? Please describe.**
Currently it assumes the first parameter. But that's a bit silly, we should use a target parameter. That would also allow pipe_input to work with other decorators cleanly.

**Describe the solution you'd like**

```python
@pipe_input(
step(...),
step(...),
target="b" # applies to parameter `b`
)
def foo(a: int, b: int) -> int:
...
```

**Describe alternatives you've considered**
Not doing this or just reordering parameters for the user.

**Additional context**
Tangentially related to this: https://github.com/DAGWorks-Inc/hamilton/pull/1160