grpcproxy: respect KeysOnly flag
grpcproxy: respect KeysOnly flag

Fixes #8478

bluebreezecf/etcd,akauppi/etcd,rnaveiras/etcd,coreos/etcd,dannysauer/etcd,visheshnp/etcd,etcd-io/etcd,mkumatag/etcd,ajityagaty/etcd,fanminshi/etcd,ajityagaty/etcd,a-robinson/etcd,mickep76/etcd,vimalk78/etcd,joshix/etcd,lorneli/etcd,mkumatag/etcd,coreos/etcd,mickep76/etcd,heyitsanthony/etcd,xiang90/etcd,sebrandon1/etcd,fanminshi/etcd,rnaveiras/etcd,bluebreezecf/etcd,etcd-io/etcd,gyuho/etcd,dannysauer/etcd,akauppi/etcd,ajityagaty/etcd,cockroachdb/etcd,sinsharat/etcd,li-ang/etcd,mqliang/etcd,YuleiXiao/etcd,gyuho/etcd,mqliang/etcd,etcd-io/etcd,glevand/coreos--etcd,mkumatag/etcd,sinsharat/etcd,visheshnp/etcd,xiang90/etcd,bdarnell/etcd,whuwxl/etcd,vimalk78/etcd,lorneli/etcd,rnaveiras/etcd,joshix/etcd,cockroachdb/etcd,sebrandon1/etcd,bdarnell/etcd,a-robinson/etcd,mqliang/etcd,glevand/coreos--etcd,li-ang/etcd,YuleiXiao/etcd,heyitsanthony/etcd,whuwxl/etcd