Export sub-sites to ZIP files

[jeffpaul]

Is your enhancement related to a problem? Please describe.
This request came in via Twitter in terms of how to further improve MU Migration.

Describe the solution you'd like

The one thing I would love to see would help bypass my script would be the ability to export all of the sub sites into their own .zip file.

Designs

n/a

Describe alternatives you've considered

n/a

Additional context

n/a

[nicholasio]

This can already be accomplished with the existing wp-cli commands by creating a bash script, e.g:

for url in $(wp site list --format=csv --fields=url | tail -n +2)
do
  wp mu-migration export all $url.zip --url=$url
done

Didn't test the code above but it should be a good starting point.

@jeffpaul Maybe add this to the readme as an example?