feat: add associated_payment_method_id to payment method session confirm response

[dmatviichuk]

…irm response

Type of Change

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

Description

Include the payment_method_id in the response returned by the payment-method-sessions/confirm endpoint.
Fixes #10573

Additional Changes

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

Motivation and Context

The /v2/payment-method-sessions/{id}/confirm endpoint returns associated_payment_methods containing temporary Redis tokens (e.g., "token_KpNynVfRrSoFound1nec"). These are for internal web SDK use and cannot be used with the proxy endpoint or other APIs that require permanent identifiers.
The proxy endpoint requires:
token_type: "payment_method_id" with a permanent payment method ID (e.g., 12345_pm_...)
token_type: "tokenization_id" with a tokenization ID (e.g., 12345_tok_...)
Since a payment method is created during session confirmation, we should include the permanent payment_method_id in the response so it can be used with the proxy endpoint and other APIs.
Use case:
After confirming a payment method session, users can now use associated_payment_method_id in the proxy endpoint:
{ "token": "12345_pm_01926c58bc6e77c09e809964e72af8c8", "token_type": "payment_method_id"}

This change is backward compatible as the new field is optional and doesn't break existing clients.

How did you test it?

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

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Changed Files

File	Status
crates/api_models/src/payment_methods.rs	0% smaller
crates/router/src/core/payment_methods.rs	0% smaller
crates/router/src/core/payment_methods/transformers.rs	0% smaller