Spanner support enhancements (#101634)

* Adds ability to run integration tests against spanner (by using GRAFANA_TEST_DB=spanner env variable. SPANNER_DB variable then specifies database to use: spannertest, emulator or string like /projects/<project>/instances/<instance>/databases/<db>)
* Adds feature to migration dialects to create database from a snapshot, instead of running individual migrations.
* Adds first version of Spanner snapshot, prepared from "OSS" migrations.
* Uses generated bit-reversed-positive values instead of auto_increment. (As an experiment)

pkg/services/sqlstore/migrator/dialect.go

@@ -6,8 +6,9 @@ import (
 	"strconv"
 	"strings"
 
-	"github.com/grafana/grafana/pkg/services/sqlstore/session"
 	"golang.org/x/exp/slices"
+
+	"github.com/grafana/grafana/pkg/services/sqlstore/session"
 	"xorm.io/xorm"
 )
 
@@ -68,6 +69,10 @@ type Dialect interface {
 	CleanDB(engine *xorm.Engine) error
 	TruncateDBTables(engine *xorm.Engine) error
 	NoOpSQL() string
+	// CreateDatabaseFromSnapshot is called when migration log table is not found.
+	// Dialect can recreate all tables from existing snapshot. After successful (nil error) return,
+	// migrator will list migrations from the log, and apply all missing migrations.
+	CreateDatabaseFromSnapshot(ctx context.Context, engine *xorm.Engine, migrationLogTableName string) error
 
 	IsUniqueConstraintViolation(err error) bool
 	ErrorMessage(err error) string
@@ -338,6 +343,10 @@ func (b *BaseDialect) CleanDB(engine *xorm.Engine) error {
 	return nil
 }
 
+func (b *BaseDialect) CreateDatabaseFromSnapshot(ctx context.Context, engine *xorm.Engine, tableName string) error {
+	return nil
+}
+
 func (b *BaseDialect) NoOpSQL() string {
 	return "SELECT 0;"
 }