op-guide: add command for checking if there's any v3 data
op-guide: add command for checking if there's any v3 data

Fixes #7681

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