default void onStartFollowing(final PeerId newLeaderId, final long newTerm) {
        // NO-OP
    }
This method is called when a follower or candidate starts following a leader and its leaderId
(should be NULL before the method is called) is set to the leader's id, situations including:
1. A candidate receives appendEntries request from a leader
2. A follower(without leader) receives appendEntries from a leader

The parameters gives the information(leaderId and term) about the very
leader whom the follower starts to follow.
User can reset the node's information as it starts to follow some leader.

@param newLeaderId the new leader id whom the follower starts to follow
@param newTerm     the new term
jraft-rheakv/rheakv-core/src/main/java/com/alipay/sofa/jraft/rhea/LeaderStateListener.java