Any entity with incomplete keys will be allocated an ID prior to insertion.
Insert by this method is non-transactional. If you need transaction
support, use {@see \Google\Cloud\Datastore\Transaction::insertBatch()}.
Example:
$entities = [
$datastore->entity('Person', ['firstName' => 'Bob']),
$datastore->entity('Person', ['firstName' => 'John'])
];
$datastore->insertBatch($entities);