feat: list payment_methods with the required fields in each method

[Chethan-rao]

Type of Change

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

Description

Currently when /payments API call is made with confirm = false from merchant server, payment is created. Assuming the customer hasn't sent the required field in this call, when a confirm API call is made, since customer has missed to send the required filed during create call, confirm call triggers an error.
So, after Payment create call is made, when payment_methods_list call will be made, along with the payment_methods we need to send the required fields for each method, so that it could be sent during confirm call.

Api changes - Added a new field required_fields in payment_method_data which lists all the required fields with its appropriate display_name, field_type and field_options.

payment_method_data: {"payment_method": {"payment_method_type": "", "required_fields": {} } }

Config changes - Added required_fields in config which is a tuple struct containing a HashMap<PaymentMethod, PaymentMethodType>. PaymentMethodType is also tuple struct containing HashMap<PaymentMethodType, ConnectorFields>. ConnectorFields is a named field struct containing HashMap<Connector, HashSet<RequiredFieldInfo>>>> and RequiredFieldInfo is a struct defined in api_models crate, containing info about each required field. The default implementation for the same is provided in defaults.rs which contains data of required fields for each payment_method and payment_method_type.

required_fields are added in defaults.rs in connector level. But while listing, it would be in payment_method_type level as we are not sure about which connector the payment is going through during confirm call. So we get a union of all required_fields of connectors for a particular payment_method_type

Additional Changes

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

Motivation and Context

To avoid failure of payments due to missing required fields

How did you test it?

Postman

Checklist

• I formatted the code cargo +nightly fmt --all
• I addressed lints thrown by cargo clippy
• I reviewed submitted code
• I added unit tests for my changes where possible
• I added a CHANGELOG entry if applicable