Allow admin to reuse existing payment sources

[rainerdema]

Introduction

The goal of this issue is to allow the creation of admin-side payments using the Solidus Stripe payment method, by reusing payment sources through the admin interface.

Current Behavior

Currently, admins can only reuse existing payment sources via the frontend and not the backend.

Desired Behavior

To allow the admin to reuse existing payment sources, a source form needs to be implemented for the Solidus Stripe Payment Method.
This would enable the reuse of payment sources within the user's wallet, preventing the use of payment methods that the user has removed from their wallet.

Additional Considerations

Since Stripe offers various payment methods beyond credit cards, partial payment-method-type views should be dedicated to each Stripe Payment Method to render the different parameters related to that specific type:
Something similar to what we're already doing for the frontend-side

Possible Problems

The current customization in Solidus does not fully support payment sources that differ from credit cards (in terms of methods and attributes nomenclature).
In the specific case of Stripe, this is incorrect since a Stripe payment method (or a payment source in Solidus) can represent many types of payments other than credit cards.

You can analyze this problem in:

• The sources passed inside the source form, which is called previous_cards
• The expected attribute in the controller called card

For now, we should adhere to this nomenclature, even though it is not customizable.

TODO

• We need to open an issue regarding the mentioned problems on Solidus: Remove references to Spree::CreditCard in admin payment views and controller solidus#5014