Allow to suspend (replica) shard allocations using a specific setting. This can help with restarting a node. The setting will be updated using the cluster update settings API, and then the node can be restarted, and once it has joined back the cluster, enable it back.

Two settings will be exposed:

• cluster.routing.allocation.disable_allocation: Allows to disable either primary or replica allocation. Note, a replica will still be promoted to primary if one does not exists.
• cluster.routing.allocation.disable_replica_allocation: Allows to disable only replica allocation.

Both settings can be updated using the cluster update settings API.