Extended Key Space support by implementing COPY command (#866)

* Added support for COPY command

* Revert getCLient signature changes, used createClient instead

Co-authored-by: Vladyslav Vildanov <vladyslavvildanov@Vladyslav-Vildanov-MacBook-Pro.local>

src/ClientContextInterface.php

@@ -18,6 +18,7 @@ use Predis\Command\CommandInterface;
 /**
  * Interface defining a client-side context such as a pipeline or transaction.
  *
+ * @method $this copy(string $source, string $destination, int $db = -1, bool $replace = false)
  * @method $this del(array|string $keys)
  * @method $this dump($key)
  * @method $this exists($key)