Some issues on the leader transfer

[absolute8511]

Currently, most raft libraries only check the commit index while doing the leader transfer. Some other cases should also be considered to avoid stale/slow read after transfer such as the snapshot status, the applied index, and the pending configure change.

related fix:
tikv/tikv#6539
tikv/tikv#8051
tikv/tikv#3878
cockroachdb/cockroach#63507
etcd-io/etcd#12163
etcd-io/etcd#12134
etcd-io/etcd#10822