Refactor payment aggregation configuration for financial products

Changes

• Updated extensions:
  • Removed payment_aggregation_scenario from FPLoanRequestConfiguration.
  • Added aggregation_scenarios array property to FPUXConfiguration with detailed aggregation scenario configurations.
  • Removed payment_aggregation_scenario from FinancialProductConfiguration under ux/default/loan_request.
  • Added new definition FinancialProductUxAggregationScenarioConfiguration including:
    • payment_aggregation_scenario: enum of processing types [MERGE_ONLY, NET_THEN_MERGE].
    • payment_aggregation_timing: enum indicating when aggregation happens (e.g., LOAN_SCHEDULE).
    • payment_types_to_net_and_merge: list of payment types applicable for net and merge aggregation.

This change removes the previous use of the PAYMENT_PREFERENCES feature flag for payment handling and introduces more granular control via the new aggregation scenarios configuration per financial product.