Summary:
This adds an optional `isConsultant` flag to `users.options`, and an endpoint that allows the support user to turn it on or off. Users marked as consultants are not counted as billable members. Follows the example of existing `allowGoogleLogin` option.
Billable members are counted when members are added or removed from a site. Changing the `isConsultant` flag has no immediate or retroactive effect on billing. The number of users in stripe is now set unconditionally, rather than only when it has changed.
Notifications to billing managers are not aware of this billing nuance, but continue to report user counts that include consultants. The notifications link users to the billing page.
Test Plan: extended test
Reviewers: georgegevoian
Reviewed By: georgegevoian
Subscribers: anaisconce, jarek
Differential Revision: https://phab.getgrist.com/D3362