Missing config_export keys and undefined method urlInfo()

Problem/Motivation

First Issue: Missing fields in config_export

In the Mailjet Subscription module, not all fields are included in `config_export`, which means the configuration isn’t saved properly or accessible within the entity object.

Second Issue:Undefined Method

When saving the form, there’s an issue with an undefined method `urlInfo()`.

Steps to Reproduce

1. Enable the Mailjet Subscription module.
2. Create a subscription.

Proposed Resolution

Fix for Missing config_export Fields

Add the missing fields in `mailjet/modules/mailjet_subscription/src/Entity/SubscriptionForm.php`.

Fix for Undefined Method

Use `toUri()` instead of `urlInfo()`, as `urlInfo()` has been deprecated. Update in `contrib/mailjet/modules/mailjet_subscription/src/Form/SubscriptionFormFormBase.php`.