Add raft log-replication status

#### Feature Description

While trying to check the stability of a Consul cluster I tried to check the status of raft log-replication to see whether all slaves had correctly received all updates and if not, by how much did they lag behind the leader.

I could not find a way to do this, the only possible interaction with the raft consensus I could find where with the `consul operator raft list-peers` and `consul operator raft remove-peer` and through the HTTP API (https://www.consul.io/api/operator/raft.html) and none of those options gave this information.

#### Use Case(s)

While I don't think this would be used on a daily basis, this could be useful to check Consul clusters and as a debug information.

If you think this could be useful, I'm willing to try to add this information available through the HTTP API and with a CLI command.