sqldb: separate migration execution from construction

This commit separates the execution of SQL and in-code migrations
from their construction. This change is necessary because,
currently, the SQL schema is migrated during the construction
phase in the lncfg package. However, migrations are typically
executed when individual stores are constructed within the
configuration builder.

lncfg/db.go

@@ -231,10 +231,10 @@ type DatabaseBackends struct {
 	// the underlying wallet database from.
 	WalletDB btcwallet.LoaderOption
 
-	// NativeSQLStore is a pointer to a native SQL store that can be used
-	// for native SQL queries for tables that already support it. This may
-	// be nil if the use-native-sql flag was not set.
-	NativeSQLStore *sqldb.BaseDB
+	// NativeSQLStore holds a reference to the native SQL store that can
+	// be used for native SQL queries for tables that already support it.
+	// This may be nil if the use-native-sql flag was not set.
+	NativeSQLStore sqldb.DB
 
 	// Remote indicates whether the database backends are remote, possibly
 	// replicated instances or local bbolt or sqlite backed databases.
@@ -449,17 +449,17 @@ func (db *DB) GetBackends(ctx context.Context, chanDBPath,
 		}
 		closeFuncs[NSWalletDB] = postgresWalletBackend.Close
 
-		var nativeSQLStore *sqldb.BaseDB
+		var nativeSQLStore sqldb.DB
 		if db.UseNativeSQL {
 			nativePostgresStore, err := sqldb.NewPostgresStore(
-				db.Postgres, sqldb.GetMigrations(),
+				db.Postgres,
 			)
 			if err != nil {
 				return nil, fmt.Errorf("error opening "+
 					"native postgres store: %v", err)
 			}
 
-			nativeSQLStore = nativePostgresStore.BaseDB
+			nativeSQLStore = nativePostgresStore
 			closeFuncs[PostgresBackend] = nativePostgresStore.Close
 		}
 
@@ -571,19 +571,18 @@ func (db *DB) GetBackends(ctx context.Context, chanDBPath,
 		}
 		closeFuncs[NSWalletDB] = sqliteWalletBackend.Close
 
-		var nativeSQLStore *sqldb.BaseDB
+		var nativeSQLStore sqldb.DB
 		if db.UseNativeSQL {
 			nativeSQLiteStore, err := sqldb.NewSqliteStore(
 				db.Sqlite,
 				path.Join(chanDBPath, SqliteNativeDBName),
-				sqldb.GetMigrations(),
 			)
 			if err != nil {
 				return nil, fmt.Errorf("error opening "+
 					"native SQLite store: %v", err)
 			}
 
-			nativeSQLStore = nativeSQLiteStore.BaseDB
+			nativeSQLStore = nativeSQLiteStore
 			closeFuncs[SqliteBackend] = nativeSQLiteStore.Close
 		}