[ENTREPRISE] Adding a balance linked to an account

Please add the option to have a balance on a user's account. This balance can be increased through purchases on the website or by using a code generated by the admin.

The balance should be used as a primary method of payment for purchases. It can also serve as a payment method if the user does not have a credit card.

It should be possible to purchase credits even if a user does not have a subscription (new user).