kvdb: add postgres

kvdb/go.mod

@@ -5,6 +5,8 @@ require (
 	github.com/btcsuite/btcwallet/walletdb v1.3.6-0.20210803004036-eebed51155ec
 	github.com/davecgh/go-spew v1.1.1 // indirect
 	github.com/google/btree v1.0.1
+	github.com/fergusstrange/embedded-postgres v1.7.0
+	github.com/jackc/pgx/v4 v4.13.0
 	github.com/lightningnetwork/lnd/healthcheck v1.0.0
 	github.com/stretchr/testify v1.7.0
 	go.etcd.io/bbolt v1.3.6
@@ -12,6 +14,7 @@ require (
 	go.etcd.io/etcd/client/pkg/v3 v3.5.0
 	go.etcd.io/etcd/client/v3 v3.5.0
 	go.etcd.io/etcd/server/v3 v3.5.0
+	golang.org/x/net v0.0.0-20210405180319-a5a99cb37ef4
 )
 
 // This replace is for https://github.com/advisories/GHSA-w73w-5m7g-f7qc