Creates a new group of conditions ORed together.
For example, consider a map entity with an 'attributes' field containing 'building_type' and 'color' columns. To find all green and red bikesheds:
$query = entity_query('map');
$group = $query
->orConditionGroup()
->condition('attributes.color', 'red')
->condition('attributes.color', 'green');
$entity_ids = $query
->condition('attributes.building_type', 'bikeshed')
->condition($group)
->execute();
Note that this particular example can be simplified:
$entity_ids = $query
->condition('attributes.color', array(
'red',
'green',
))
->condition('attributes.building_type', 'bikeshed')
->execute();
\Drupal\Core\Entity\Query\ConditionInterface
public function orConditionGroup();