fix(connector): use enum to deserialize latest_charge in stripe psync response

[hrithikesh026]

Type of Change

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

Description

Stripe webhook body deserialization was failing due to latest_charge field in PaymentIntentSyncResponse.
stripe sends one of the following type in that field:

• String(latest_charge_id)
• Null
• LatestCharge json object
  Out of above 3, String response was not handled. This was causing deserialization error during webhooks for bank redirect. and bank debit.
  latest_charge field is being used to populate connector_mandate_id in the DB for bank redirect recurring payment in stripe. But in webhook body, this field is a string(latest_charge_id).

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?

Manual

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