Support SCIM

[fflorent]

SCIM is a standard way to provision or deprovision users to a Service Provider (like Grist) as requested by an Identity Provider.

This could let the IdP to do the following on Grist:

• create accounts for users and start assigning them access without waiting for them to connect the first time on Grist;
• delete accounts and/or revoke access from organizations (and maybe workspaces);
• change user informations in Grist;

It requires to implement a REST API that complies with the spec (see below).

IETF RFC (spec): https://www.rfc-editor.org/rfc/rfc7644 Okta resource: https://developer.okta.com/docs/concepts/scim/