CHANGELOG: Add 3.4 changelog entry for lease checkpointing feature

CHANGELOG-3.4.md

@@ -43,6 +43,7 @@ See [code changes](https://github.com/coreos/etcd/compare/v3.3.0...v3.4.0) and [
 - Improve [functional tester](https://github.com/coreos/etcd/tree/master/functional) coverage: [proxy layer to run network fault tests in CI](https://github.com/coreos/etcd/pull/9081), [TLS is enabled both for server and client](https://github.com/coreos/etcd/pull/9534), [liveness mode](https://github.com/coreos/etcd/issues/9230), [shuffle test sequence](https://github.com/coreos/etcd/issues/9381), [membership reconfiguration failure cases](https://github.com/coreos/etcd/pull/9564), [disastrous quorum loss and snapshot recover from a seed member](https://github.com/coreos/etcd/pull/9565), [embedded etcd](https://github.com/coreos/etcd/pull/9572).
 - Improve [index compaction blocking](https://github.com/coreos/etcd/pull/9511) by using a copy on write clone to avoid holding the lock for the traversal of the entire index.
 - Update [JWT methods](https://github.com/coreos/etcd/pull/9883) to allow for use of any supported signature method/algorithm.
+- Add [Lease checkpointing](https://github.com/coreos/etcd/pull/9924) to persist remaining TTLs to the consensus log periodically so that long lived leases progress toward expiry in the presence of leader elections and server restarts.
 
 ### Breaking Changes