Only the first scheduler job of a page gets its status saved and is registered automatically

Closing as Won't Fix, following a discussion on the #xwiki Matrix room.

The proposed fix (https://github.com/xwiki/xwiki-platform/pull/6884) made the backend handle every job object of a page (status, startup restore, page events). The decision is to not go in that direction: the scheduler UI (Scheduler.WebHome, XWiki.SchedulerJobSheet) has never supported several jobs per page, several jobs per page never fully worked, so it's very unlikely to be used, and the preferred direction is rather to make "one scheduler job per page" the official model than to fix the multi-job support in the backend only.

Note that the current behaviour described in this issue remains: scheduleJobs(Document) still schedules every job object of a page while the rest of the scheduler only handles the first one. Making the one-job-per-page model explicit in the API is a separate topic, to be discussed on the forum if needed.