Add DatabaseCredentials class and implement database picker question

config/services.yaml

@@ -24,7 +24,7 @@ services:
     # add more service definitions when explicit configuration is needed
     # please note that last definitions always *replace* previous ones
 
-    App\Service\MysqliConnection:
+    App\Service\DatabaseCredentials:
         arguments:
             $hostname: '%env(string:DATABASE_HOSTNAME)%'
             $user: '%env(string:DATABASE_USER)%'