CHANGELOG: backport quota size limit metrics

Signed-off-by: Gyuho Lee <gyuhox@gmail.com>

CHANGELOG-3.1.md

@@ -16,6 +16,7 @@ See [code changes](https://github.com/coreos/etcd/compare/v3.1.18...v3.1.19) and
 Note that any `etcd_debugging_*` metrics are experimental and subject to change.
 
 - Add [`etcd_server_slow_read_indexes_total`](https://github.com/coreos/etcd/pull/9897) Prometheus metric.
+- Add [`etcd_server_quota_backend_bytes`](https://github.com/coreos/etcd/pull/9820) Prometheus metric.
 
 
 ## [v3.1.18](https://github.com/coreos/etcd/releases/tag/v3.1.18) (2018-06-15)

CHANGELOG-3.2.md

@@ -15,6 +15,7 @@ See [code changes](https://github.com/coreos/etcd/compare/v3.2.23...v3.2.24) and
 Note that any `etcd_debugging_*` metrics are experimental and subject to change.
 
 - Add [`etcd_server_slow_read_indexes_total`](https://github.com/coreos/etcd/pull/9897) Prometheus metric.
+- Add [`etcd_server_quota_backend_bytes`](https://github.com/coreos/etcd/pull/9820) Prometheus metric.
 
 ### gRPC Proxy
 

CHANGELOG-3.3.md

@@ -16,6 +16,7 @@ See [code changes](https://github.com/coreos/etcd/compare/v3.3.8...v3.3.9) and [
 Note that any `etcd_debugging_*` metrics are experimental and subject to change.
 
 - Add [`etcd_server_slow_read_indexes_total`](https://github.com/coreos/etcd/pull/9897) Prometheus metric.
+- Add [`etcd_server_quota_backend_bytes`](https://github.com/coreos/etcd/pull/9820) Prometheus metric.
 
 
 ## [v3.3.8](https://github.com/coreos/etcd/releases/tag/v3.3.8) (2018-06-15)