Allow `schema` as parameter to `init_series`

- As a user, I wish I could use `ww.init_series` to initialize a series with an existing woodwork column schema. It's possible to do with with `series.ww.init`, and it'd be nice to be able to do the same when the series' dtype will have to change and we need to use
- the`init_series` util

#### Code Example

```python
series = pd.Series(...)
ww_series = ww.init_series(schema=schema)
```