CHANGELOG-3.4: highlight new metrics, histogram upper bound changes
CHANGELOG-3.4: highlight new metrics, histogram upper bound changes

Signed-off-by: Gyuho Lee <3454051ee3341eb69bdf6fca40899cdad4d86496@gmail.com>

sinsharat/etcd,li-ang/etcd,glevand/coreos--etcd,mqliang/etcd,mqliang/etcd,cockroachdb/etcd,etcd-io/etcd,coreos/etcd,rnaveiras/etcd,vimalk78/etcd,rnaveiras/etcd,joshix/etcd,mkumatag/etcd,glevand/coreos--etcd,li-ang/etcd,mkumatag/etcd,bdarnell/etcd,sebrandon1/etcd,gyuho/etcd,sinsharat/etcd,sebrandon1/etcd,vimalk78/etcd,gyuho/etcd,bdarnell/etcd,etcd-io/etcd,xiang90/etcd,dannysauer/etcd,etcd-io/etcd,cockroachdb/etcd,dannysauer/etcd,ajityagaty/etcd,xiang90/etcd,joshix/etcd,ajityagaty/etcd,mkumatag/etcd,ajityagaty/etcd,mqliang/etcd,coreos/etcd,rnaveiras/etcd