Record Ticket Satisfaction

migrations/0468: the one door a satisfaction rating comes in through.

⛔NOT A SURVEY ENDPOINT, and deliberately not reachable by an anonymous customer following a link: gated exactly like every other write on a ticket (_require_kind_grant_or_assignee -- the caller must hold this ticket's kind or already own it). WHO asks the customer, and how their answer gets from them to here, is a product decision nobody has made; building an unauthenticated rating link would be making it. Until it is made, the honest writer is a person who was told -- which is exactly why rated_by distinguishes 'customer' from 'manager' and the two are never averaged (0276's rule, kept here rather than restated differently).