Spanner-related fixes (#102376)

* Fix UNION syntax in resourcepermissions package.
* Fix migrations in usermig package to work with Spanner.
* Fix health query.
* Use more connections for integration tests.
* Add test-go-integration-spanner target to run integration tests against Spanner emulator.
* Add test for enterprise.
* Don't delete sequence number for migration_log.id column.

* Only bump max open connections to 20 for Spanner.
Lower integration test timeout.

pkg/services/accesscontrol/resourcepermissions/store.go

@@ -449,7 +449,7 @@ func (s *store) getResourcePermissions(sess *db.Session, orgID int64, query GetR
 	builtin := builtinSelect + builtinFrom + where
 	args = append(args, args[:initialLength]...)
 
-	sql := userQuery + " UNION " + team + " UNION " + builtin
+	sql := userQuery + " " + s.sql.GetDialect().UnionDistinct() + " " + team + " " + s.sql.GetDialect().UnionDistinct() + " " + builtin
 	queryResults := make([]flatResourcePermission, 0)
 	if err := sess.SQL(sql, args...).Find(&queryResults); err != nil {
 		return nil, err