Add getters and setters for attributes property

This addition prevents the need to overload the $attributes property when extending this class to get access to all attributes at once. Currently, there is no way to get all attributes out of the passport without knowing the names of each attribute. 

hslavich/OneloginSamlBundle#181 (comment)

Author: pluk77

Authenticator/Passport/Passport.php

@@ -103,4 +103,9 @@ public function getAttribute(string $name, $default = null)
     {
         return $this->attributes[$name] ?? $default;
     }
+
+    public function getAttributes(): array
+    {
+        return $this->attributes;
+    }
 }