Add payment aggregation scenario configuration to Flex loan product

Changes

• No API endpoint changes.
• Configuration schema updated:
  • Added the payment_aggregation_scenario property to FPLoanRequestConfiguration to define the processing type for aggregation scenarios. Possible values include MERGE_ONLY and NET_THEN_MERGE.
  • Added the payment_aggregation_scenario property into the FinancialProductConfiguration under ux.default.loan_request for Flex loans.

These changes enable configuring payment and deposit aggregation scenarios in the Flex financing product, allowing for faster payment processing during loan validation.