Summary:
The summary includes a count of documents that are approaching
limits, in grace period, or delete-only. The endpoint is only accessible
to site owners, and is currently unused. A follow-up diff will add usage
banners to the site home page, which will use the response from the
endpoint to communicate usage information to owners.
Test Plan: Browser and server tests.
Reviewers: alexmojaki
Reviewed By: alexmojaki
Differential Revision: https://phab.getgrist.com/D3420
