Major Description
The way the critical thread liveness check is configured has a number of usability issues.
1) By default, the liveness check is disabled (i.e. if no failure handler is specified in the configuration). However, if you specify any handler (including the default one), liveness check gets enabled (which is something the users may not want) unless you disable it explicitly.
2) Users that use Ignite 2.6 with a configured failure handler will get this check enabled after migrating to Ignite 2.7.
In the two cases above, the functionality changes in a non-trivial way. Ideally, we need an option that enables this functionality explicitly. A possible example would be to keep liveness check disabled until the user sets the systemWorkerBlockedTimeout to a positive value. (Or the other way around: enable liveness check by default until the user explicitly disables it).
