ENH: unify signature for df.update and Series.update
Currently, there's

```DataFrame.update(other, join='left', overwrite=True, filter_func=None, raise_conflict=False)```
and 
```Series.update(other)```

I think Series should have the same keywords/capabilities, and ideally share the implementation, probably in `generic.py`. Relevant also in light of #22286 and #21855.