feat(router): make the billing country for apple pay as optional field

[ShankarSinghC]

Type of Change

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

Description

This pr contains the changes to make the billing country for apple pay as optional field. In this case if a billing country is not passed in the payments create call the session call would still be done and the billing country would be collected form sdk during the payments confirm.

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?

Test Case :-
This flow needs to be tested for stripe (Manual and simplified flow), trustpay, bluesanp, payme and any important connectors for which apple pay is implemented.

1. Create a apple pay payment with confirm false without apple the country in billing address
2. Make a Session token call. Expected behaviour is response should contain session token for apple pay with the country_code as null.

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