Dedicated liveness endpoint for K8 liveness probe

Until now, the K8 liveness probe has been relying on api/system/health status. This approach has several drawbacks:

• During safe mode, the status is red (=SonarQube is not usable). But in the context of a liveness probe, we want a safe mode to be considered alive
• On DCE, the health is the health of the cluster, not of the node. it's not accurate enough, and the K8 scheduler would reschedule healthy nodes because "the cluster is red".

How:

• remove "local" parameter on api/system/health that was introduced previously, it's replaced by api/system/liveness
• create api/system/liveness endpoint, that return HTTP code 204 if the node is alive, and should not be killed:
  • Not a standalone setup (DCE multi-node): web process is green, CE process is green, DB is reachable
  • Standalone setup (CE/DE/EE or DCE single-node): web process is green, CE process is green, DB is reachable, ES is not red
  • any HTTP code outside of the range 200-299 means that the node should be killed and rescheduled
  • For all editions, on Safe Mode, only the database connexion is check
  • this new endpoint should support the same system passcode as api/system/health (X-Sonar-Passcode)