fix(payment_methods): unmask last4 digits of card when listing payment methods for customer

[Chethan-rao]

Type of Change

• Bugfix
• New feature
• Enhancement
• Refactoring
• Dependency updates
• Documentation
• CI/CD

Description

When metadata of a saved card is updated and customer payment methods are listed, the updated card's last 4 digit is getting masked in the response. This PR unmasks it and returns the raw digits.

Bug: last4_digits is masked -

Fix: unmasked -

Additional Changes

• This PR modifies the API contract
• This PR modifies the database schema
• This PR modifies application configuration/environment variables

Motivation and Context

How did you test it?

1. Save a card in locker
2. Change the metadata of the saved card and try to save it again in locker
3. Now when list_customer_payment_method is called, the last4_digits field of the updated card has to be unmasked

Checklist

• I formatted the code cargo +nightly fmt --all
• I addressed lints thrown by cargo clippy
• I reviewed the submitted code
• I added unit tests for my changes where possible
• I added a CHANGELOG entry if applicable