multi: freeze graph SQL migration logic

Copy over all the code that the graph SQL migration needs to a
separate folder. This will let us advance the main graph SQL CRUD code
without worrying about changing the sql migration code. It will also let
us change the SQL queries without changing the migration. In this
commit, only the migration logic is "frozen" but in an upcoming commit,
the sqlc queries & models will be frozen too.

graph/db/migration1/log.go

@@ -0,0 +1,31 @@
+package migration1
+
+import (
+	"github.com/btcsuite/btclog/v2"
+	"github.com/lightningnetwork/lnd/build"
+)
+
+// Subsystem defines the logging code for this subsystem.
+const Subsystem = "GRDB"
+
+// log is a logger that is initialized with no output filters.  This
+// means the package will not perform any logging by default until the caller
+// requests it.
+var log btclog.Logger
+
+func init() {
+	UseLogger(build.NewSubLogger(Subsystem, nil))
+}
+
+// DisableLog disables all library log output.  Logging output is disabled
+// by default until UseLogger is called.
+func DisableLog() {
+	UseLogger(btclog.Disabled)
+}
+
+// UseLogger uses a specified Logger to output package logging info.
+// This should be used in preference to SetLogWriter if the caller is also
+// using btclog.
+func UseLogger(logger btclog.Logger) {
+	log = logger
+}