* Replace interval-hours and anchor-time with cron

Removed the two settings and replaced with a single cron schedule setting

Renamed the /set-interval endpoint to /set-refresh-schedule

* Ignore "year" part in schedule endpoint

* Fix variable

* Use a temp scheduler and initialize the refresh job

Running into errors when updating the triggers for each database's
refresh job because the "job" itself didn't exist. Reminder of what's
going on here: There's a single refresh job. It has a trigger for each
database. So updating the trigger would fail since it doesn't exist
since there was no job to hold the triggers.

This error is quite clear in the tests run locally:

```
ERROR in metabase.api.persist-test/set-refresh-schedule-test (util.clj:421)
Uncaught exception, not in assertion.

        clojure.lang.ExceptionInfo: Error in with-temporary-setting-values: Couldn't store trigger 'DEFAULT.metabase.task.PersistenceRefresh.database.trigger.1' for 'DEFAULT.metabase.task.PersistenceRefresh.job' job:The job (DEFAULT.metabase.task.PersistenceRefresh.job) referenced by the trigger does not exist.
    location: metabase.public-settings/persisted-models-enabled
     setting: "persisted-models-enabled"
       value: true
```

But this logging is absent from the logging in Github annoyingly:

```
FAIL in metabase.api.persist-test/set-refresh-schedule-test (persist_test.clj:26)
Setting new cron schedule reschedules refresh tasks
Setting :persisted-models-enabled = true
expected: "0 0 0/12 * * ? *"
  actual: (nil)
```
Whic doesn't give us the error, just the test result.

* update to newer API `set-interval` -> `set-refresh-schedule`

```
;; old
{:hours 4}

;; new
{:cron "0 0 0/1 * * ? *"}
```

Co-authored-by: Case Nelson <case@metabase.com>
Co-authored-by: dan sutton <dan@dpsutton.com>