[8.x] Make it possible to use prefixes on Predis per Connection (#40083)

* Make it possible to set prefix per connection

* Fix formatting

* Add new code to connect to cluster as well

* Use isset instead of empty

To allow the use of zero. Change the function from empty to isset

src/Illuminate/Redis/Connectors/PredisConnector.php

@@ -23,6 +23,10 @@ public function connect(array $config, array $options)
             ['timeout' => 10.0], $options, Arr::pull($config, 'options', [])
         );
 
+        if (isset($config['prefix'])) {
+            $formattedOptions['prefix'] = $config['prefix'];
+        }
+
         return new PredisConnection(new Client($config, $formattedOptions));
     }
 
@@ -38,6 +42,10 @@ public function connectToCluster(array $config, array $clusterOptions, array $op
     {
         $clusterSpecificOptions = Arr::pull($config, 'options', []);
 
+        if (isset($config['prefix'])) {
+            $clusterSpecificOptions['prefix'] = $config['prefix'];
+        }
+
         return new PredisClusterConnection(new Client(array_values($config), array_merge(
             $options, $clusterOptions, $clusterSpecificOptions
         )));