feat(payment_link): Add support for saved payment method option for payment link

[sahkal]

Type of Change

• New feature

Description

Currently we don't allow customer saved payment method button to be displayed in payment link, with this change merchant will be able to enable saved payment method option.

Additional Changes

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

added enabled_saved_payment_method in payment_link_config object

Motivation and Context

How did you test it?

Do payments Create using the following curl, generate payment link and look for saved payment method option in the sdk.

Pass the same customer_id again and check if saved payment method is visible for the following customer in subsequent payment links

curl --location 'http://localhost:8080/payments' \
--header 'Content-Type: application/json' \
--header 'Accept: application/json' \
--header 'api-key: dev_AuHSsPcx0ehbYzSjR9pKwLNS50cMLhGLNNy5sCNXFiIGgZHo44UW53nLzGe6W1ho' \
--data-raw '{
    "amount": 250,
    "currency": "USD",
    "customer_id": "StripeCustomer",
    "email": "[email protected]",
    "name": "John Doe",
    "phone": "999999999",
    "phone_country_code": "+65",
    "description": "Please Pay for your XYZ",
    "authentication_type": "no_three_ds",
    "return_url": "https://google.com",
    "setup_future_usage": "on_session",
    "payment_link":true,
    "payment_link_config": {
        "theme": "#0C581D", 
        "enabled_saved_payment_method":true
    },
    "order_details": [
        {
            "product_name": "Tea",
            "quantity": 1,
            "amount": 110,
            "product_img_link": "https://thumbs.dreamstime.com/b/indian-tea-spices-masala-chai-33827904.jpg"
        },
        {
            "product_name": "Tea",
            "quantity": 20,
            "amount": 110,
            "product_img_link": "https://thumbs.dreamstime.com/b/indian-tea-spices-masala-chai-33827904.jpg"
        },
        {
            "product_name": "Tea",
            "quantity": 1,
            "amount": 110,
            "product_img_link": "https://thumbs.dreamstime.com/b/indian-tea-spices-masala-chai-33827904.jpg"
        }
    ],
    "billing": {
        "address": {
            "zip": "94122",            
            "first_name": "sahkal",
            "last_name": "poddar"
        }
    }
}
'

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