Set a time zone on users, graphs, and projects
You can now store an optional IANA time zone (for example America/New_York)
on a user or graph, and set a project-wide default time zone. Pass time_zone
when creating or updating a user or graph, and default_time_zone when updating
your project. On update, omitting the field preserves the current value, a
string sets it, and null clears it. Invalid or non-IANA values are rejected.