/**
  * Add an index to a database table. In $options you can specify unique = true/false or name (index name).
  *
  * @param string $columns
  * @param array  $options
  *
  * @return $this
  */
 public function addIndex($columns, $options = [])
 {
     $this->table->addIndex($columns, $options);
     return $this;
 }