[Healthcheck] Invalid tracker events

[vahonc]

Transform the current System message about invalid tracker events in an Healthcheck.

https://github.com/Smile-SA/elasticsuite/blob/2.11.x/src/module-elasticsuite-tracker/Model/System/Message/WarningAboutInvalidTrackerEvents.php

The criticity should be "notice" if there are less than 10.000, and warning if more.