Add time to survive timeout to cluster safety job

Add a configurable 'time to survive after split brain' parameter for clusters. This will be used to pause the cluster safety job if a likely split brain is detected, ie if the cluster safety job has run on this instance before (meaning it's not the first run after startup), but the cluster safety number cannot be found in the cache.

In this scenario, the cluster safety job will wait for the configured time-to-survive, to allow the nodes to rejoin. After this time has passed, if the node still cannot find the cluster safety number in the cache, the node will panic.