lnd: introduce separate payment db on the server level.

We add a new payment db instance on the server level. Which we
will you for the payment related queries in a following commit.

Author: ziggie1984

config_builder.go

@@ -924,6 +924,10 @@ type DatabaseInstances struct {
 	// InvoiceDB is the database that stores information about invoices.
 	InvoiceDB invoices.InvoiceDB
 
+	// KVPaymentsDB is the database that stores all payment related
+	// information.
+	KVPaymentsDB *channeldb.KVPaymentsDB
+
 	// MacaroonDB is the database that stores macaroon root keys.
 	MacaroonDB kvdb.Backend
 
@@ -1184,6 +1188,14 @@ func (d *DefaultDatabaseBuilder) BuildDatabase(
 		dbs.InvoiceDB = dbs.ChanStateDB
 	}
 
+	// Mount the payments DB which is only KV for now.
+	//
+	// TODO(ziggie): Add support for SQL payments DB.
+	kvPaymentsDB := channeldb.NewKVPaymentsDB(
+		dbs.ChanStateDB,
+	)
+	dbs.KVPaymentsDB = kvPaymentsDB
+
 	// Wrap the watchtower client DB and make sure we clean up.
 	if cfg.WtClient.Active {
 		dbs.TowerClientDB, err = wtdb.OpenClientDB(

server.go

@@ -317,6 +317,12 @@ type server struct {
 
 	invoicesDB invoices.InvoiceDB
 
+	// kvPaymentsDB is the DB that contains all functions for managing
+	// payments.
+	//
+	// TODO(ziggie): Replace with interface.
+	kvPaymentsDB *channeldb.KVPaymentsDB
+
 	aliasMgr *aliasmgr.Manager
 
 	htlcSwitch *htlcswitch.Switch
@@ -1081,9 +1087,7 @@ func newServer(cfg *Config, listenAddrs []net.Addr,
 		PathFindingConfig:   pathFindingConfig,
 	}
 
-	paymentControl := channeldb.NewKVPaymentsDB(dbs.ChanStateDB)
-
-	s.controlTower = routing.NewControlTower(paymentControl)
+	s.controlTower = routing.NewControlTower(dbs.KVPaymentsDB)
 
 	strictPruning := cfg.Bitcoin.Node == "neutrino" ||
 		cfg.Routing.StrictZombiePruning