refactor(card): use `billing.first_name` instead of `card_holder_name`

[Narayanbhat166]

Type of Change

• [x] Refactoring

Description

This PR includes changes to use billing.first_name and billing.last_name instead of payment_method_data.[card].card_holder_name at the connector level. The backwards compatibility is provided.

So billing.first_name will be used instead of card_holder_name in the connectors.

Additional Changes

• [x] This PR modifies the API contract

Motivation and Context

How did you test it?

• Added unit tests
• Create a payment of stripe connector, and check the data in stripe dashboard.

Checklist

• [x] I formatted the code cargo +nightly fmt --all
• [x] I addressed lints thrown by cargo clippy
• [x] I reviewed the submitted code
• [x] I added unit tests for my changes where possible