Implement key parameter on cache tag (#2589)

Author: Duncan McClean

src/Tags/Cache.php

@@ -34,6 +34,10 @@ private function isEnabled()
 
     private function getCacheKey()
     {
+        if ($this->params->has('key')) {
+            return $this->params->get('key');
+        }
+
         $hash = [
             'content' => $this->content,
             'params' => $this->params->all(),