feat: init migrations for transactional tables (#9946)

# Which Problems Are Solved

To start with transactional tables we need to setup the new `zitadel`
schema in a way that does not rely on the event store later.

# How the Problems Are Solved

Setup step added which calls the function which executes the migrations.

# Additional Changes

none

# Additional Context

- closes #9933

backend/v3/storage/database/dialect/postgres/migration/migrationgs.go

@@ -0,0 +1,33 @@
+package migration
+
+import (
+	"context"
+
+	"github.com/jackc/pgx/v5"
+	"github.com/jackc/tern/v2/migrate"
+)
+
+var migrations []*migrate.Migration
+
+func Migrate(ctx context.Context, conn *pgx.Conn) error {
+	// we need to ensure that the schema exists before we can run the migration
+	// because creating the migrations table already required the schema
+	_, err := conn.Exec(ctx, "CREATE SCHEMA IF NOT EXISTS zitadel")
+	if err != nil {
+		return err
+	}
+	migrator, err := migrate.NewMigrator(ctx, conn, "zitadel.migrations")
+	if err != nil {
+		return err
+	}
+	migrator.Migrations = migrations
+	return migrator.Migrate(ctx)
+}
+
+func registerSQLMigration(sequence int32, up, down string) {
+	migrations = append(migrations, &migrate.Migration{
+		Sequence: sequence,
+		UpSQL:    up,
+		DownSQL:  down,
+	})
+}