Chore: Add initial/experimental xorm spanner driver (#101398)

* make it build and start

* run some migrations

* add build tags, remove log

* remove unused code

* revert go.mod changes

* move initialisation into dialect file

* update workspace

* update workspace once again

* clean up dependencies

* further cleanup

* Address some review feedback.

* Fix go.sum.

---------

Co-authored-by: Peter Štibraný <pstibrany@gmail.com>

pkg/services/sqlstore/migrator/migrator.go

@@ -400,6 +400,11 @@ func (mg *Migrator) InTransaction(callback dbTransactionFunc) error {
 	sess := mg.DBEngine.NewSession()
 	defer sess.Close()
 
+	// XXX: Spanner cannot execute DDL statements in transactions
+	if mg.Dialect.DriverName() == Spanner {
+		return callback(sess)
+	}
+
 	if err := sess.Begin(); err != nil {
 		return err
 	}