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/sqlutil/sqlutil.go

@@ -6,6 +6,8 @@ import (
 	"io/fs"
 	"os"
 	"path/filepath"
+
+	"cloud.google.com/go/spanner/spannertest"
 )
 
 // ITestDB is an interface of arguments for testing db
@@ -42,6 +44,8 @@ func GetTestDB(dbType string) (*TestDB, error) {
 		return postgresTestDB()
 	case "sqlite3":
 		return sqLite3TestDB()
+	case "spanner":
+		return spannerTestDB()
 	}
 
 	return nil, fmt.Errorf("unknown test db type: %s", dbType)
@@ -151,3 +155,49 @@ func postgresTestDB() (*TestDB, error) {
 		Cleanup:    func() {},
 	}, nil
 }
+
+func spannerTestDB() (*TestDB, error) {
+	// See https://github.com/googleapis/go-sql-spanner/blob/main/driver.go#L56-L81 for connection string options.
+
+	spannerDB := os.Getenv("SPANNER_DB")
+	if spannerDB == "" {
+		return nil, errors.New("SPANNER_DB environment variable not set")
+	}
+
+	if spannerDB == "spannertest" {
+		// Start in-memory spannertest instance.
+		srv, err := spannertest.NewServer("localhost:0")
+		if err != nil {
+			return nil, err
+		}
+
+		return &TestDB{
+			DriverName: "spanner",
+			ConnStr:    fmt.Sprintf("%s/projects/grafanatest/instances/grafanatest/databases/grafanatest;usePlainText=true", srv.Addr),
+			Cleanup:    srv.Close,
+		}, nil
+	}
+
+	if spannerDB == "emulator" {
+		host := os.Getenv("SPANNER_EMULATOR_HOST")
+		if host == "" {
+			host = "localhost:9010"
+		}
+
+		// To create instance and database manually, run:
+		//
+		//  $ curl "localhost:9020/v1/projects/grafanatest/instances" --data '{"instanceId": "'grafanatest'"}'
+		//  $ curl "localhost:9020/v1/projects/grafanatest/instances/grafanatest/databases" --data '{"createStatement": "CREATE DATABASE `grafanatest`"}'
+		return &TestDB{
+			DriverName: "spanner",
+			ConnStr:    fmt.Sprintf("%s/projects/grafanatest/instances/grafanatest/databases/grafanatest;usePlainText=true", host),
+			Cleanup:    func() {},
+		}, nil
+	}
+
+	return &TestDB{
+		DriverName: "spanner",
+		ConnStr:    spannerDB,
+		Cleanup:    func() {},
+	}, nil
+}