[Job Launcher] Billing system - Create Endpoint to List Payment Methods

[flopez7]

Description
Create an endpoint to list all payment methods associated with the user by obtaining the userId from auth token and retrieving the user’s payment methods from Stripe.

Motivation
Allow users to view their stored payment methods conveniently.

Implementation details

• Get userId from token and retrieve customerId from the user record.
• Fetch payment methods linked to customerId from Stripe and return them.