With current implement, a MsgHeartbeat do these things:

• update( or correct ) a peer's status like commit index, StateRole, ect.
• confirm quorum for quorum check or read index request

While the MsgAppend already do the first, and the second are also easy to done
by attach the ctx with MsgAppend, we can reduce MsgHeartbeat by :

1. when sending a MsgAppend check if the heartbeat_elapsed reach a threshold
2. if it does reset the heartbeat_elapsed and attach the ctx on this msg if there is one

is it possible to implement and improve a bit performance ?