ENH: Add `method='table'` for EWM.mean
- [x] tests added / passed
- [x] Ensure all linting tests pass, see [here](https://pandas.pydata.org/pandas-docs/dev/development/contributing.html#code-standards) for how to run them
- [x] whatsnew entry

@meeseeksdev backport 1.3.x thanks @mroeschke  Something went wrong ... Please have  a look at my logs. This is failing ci. reverting to get ci back to green

@mroeschke can you open a new PR for this.