Summary:
Tutorials are now hidden by default in grist-core and grist-ee, and can
be re-enabled via a new env variable, GRIST_UI_FEATURES, which accepts
a comma-separated list of UI features to enable.
Test Plan: Browser tests.
Reviewers: jarek
Reviewed By: jarek
Subscribers: jarek
Differential Revision: https://phab.getgrist.com/D3885
