feat(router): added merchant custom name support for payment link

[sahkal]

Type of Change

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

Description

Add merchant custom name support for payment link

Additional Changes

• This PR modifies the API contract
• This PR modifies the database schema
• This PR modifies application configuration/environment variables
  "payment_link_object": { "link_expiry" : "2025-10-09T16:23:10Z", "merchant_custom_domain_name": null, "custom_merchant_name": "sahkal" }

Motivation and Context

How did you test it?

Tested locally

Testing Curl

curl --location 'http://localhost:8080/payments' \ --header 'Content-Type: application/json' \ --header 'Accept: application/json' \ --header 'api-key: dev_bKPPICtnI7RGJVIg97fO3Vzejk87kpO2Cggy9MULP3FcXxeQkFBHdHS6buRmk0ty' \ --data '{ "amount": 3423, "currency": "USD", "confirm": false, "customer_id": "sahkal", "return_url": "https://google.com", "description": "For selling Tea", "order_details": [ { "product_name": "Tea", "quantity": 1, "amount": 10, "product_img_link": null }, { "product_name": "Tea", "quantity": 1, "amount": 10, "product_img_link": "https://thumbs.dreamstime.com/b/indian-tea-spices-masala-chai-33827904.jpg" }, { "product_name": "Tea", "quantity": 1, "amount": 10, "product_img_link": "https://thumbs.dreamstime.com/b/indian-tea-spices-masala-chai-33827904.jpg" }, { "product_name": "Tea", "quantity": 1, "amount": 10, "product_img_link": "https://thumbs.dreamstime.com/b/indian-tea-spices-masala-chai-33827904.jpg" }, { "product_name": "Tea", "quantity": 1, "amount": 10, "product_img_link": "https://thumbs.dreamstime.com/b/indian-tea-spices-masala-chai-33827904.jpg" } ], "payment_link_object": { "link_expiry": "2025-10-09T16:23:10Z", "merchant_custom_domain_name": null, "custom_merchant_name": "sahkal" } }'

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

[jarnura]

LGTM