Allow `schema` as parameter to `init_series`

[tamargrey]

• 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
• theinit_series util

Code Example

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