Generating multiple stylesheets on save

[jamieschmid]

Is your feature request related to a problem? Please describe.
Since WP introduced the block editor, there is now a need to carry frontend styles into the admin. However, since we don't want to style ALL of the admin controls and just the editor, this requires generating a separate stylesheet where you are able to include/exclude certain styles which may cause issues in the admin.

Describe the solution you'd like
An easy way to add additional stylesheets to be compiled with style.css, and being able to define which SASS master file to compile.
This issue is related and has some details and progress: #103
This PR has been built to compile them into separate directories which is also cool: #125

Describe alternatives you've considered
I've set up my own solution manually but it was not the most efficient. Subsequent node/npm updates broke my implementation. It would be awesome to have official WPGulp support for this feature!

[jmccall75]

I'd love to see this too.