Update user information

Updates a user's profile. Only firstName, lastName, and timezone are mutable through this endpoint — other profile fields are ignored. The body must contain at least one of those three (a request that touches none returns 400).

A regular user can only edit their own profile. To edit someone else's, the caller must either be a system or eLab admin, or be in the same subgroup as the target and hold the User.Update permission. Updating an unknown user returns 404 from the lookup.