Summary:
This adds a `site:delete` target to `cli.sh` for deleting sites. Sites should be specified by numeric org id, and for confirmation their name also needs to be given.
All the docs in the site are deleted permanently, and the workspaces, and the site, and the stripe customer (if any).
Test Plan: manual
Reviewers: dsagal
Reviewed By: dsagal
Differential Revision: https://phab.getgrist.com/D3015
