Core: Add extra write consistency validation

Add additional optional validation on top of the write consistency check. After the cluster state write validation check we have today, an optional extra write consistency validation may happens that actually goes the nodes containing the shard copies and verifies if that nodes are in a started state.

Note: this PR is based on improve_zen branch
can we use `in.readOptionalBoolean` and the respective `writeOptionalBoolean on the writeTo side?