Creator sentiment emails iterate (#40922)

* Send creator emails every week

mod the email by 52 instead of by 12 and use the current week as an
anchor

```clojure
user=> (require '[java-time.api :as t])
nil
user=> (let [every-day (take 1000 (t/iterate t/plus (t/local-date 2024 1 1) (t/days 1)))
             f         (fn [d]
                         (let [wf (java.time.temporal.WeekFields/of (java.util.Locale/getDefault))]
                           (.get d (.weekOfWeekBasedYear wf))))]
         (sort (keys (frequencies (map f every-day)))))
(1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21
 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39
 40 41 42 43 44 45 46 47 48 49 50 51 52)
```

```clojure
user=> (metabase.util.cron/cron-string->schedule-map "0 0 2 ? * 7")
{:schedule_minute 0,
 :schedule_day "sat",
 :schedule_frame nil,
 :schedule_hour 2,
 :schedule_type "weekly"}
```

* fix typo in creator sentiment email, clean up a bit

typo: had `:verison` instead of `version`.

And while I'm in there, make the payload all in one file and have the
email namespace json->bytes->b64-encode so the data is all in one place
and the setting that allows it to be present or not is co-located.