Add Methods for Assigning and Creating Dedicated Virtual Accounts (DVA)

[PrevailExcel]

This PR introduces two new methods to enhance the functionality of managing dedicated virtual accounts (DVA) for customers. The methods are:

1. assignDedicatedAccount
   Allows assigning a dedicated virtual account to a customer.
   The method creates a customer (if not already existing), validates the customer, and assigns a DVA.
   Accepts an optional array of data or defaults to fetching relevant inputs from the request object.

2. createDedicatedAccount
   Enables the creation of a dedicated virtual account for an existing customer.
   Accepts an optional array of data or defaults to fetching relevant inputs from the request object.

References

No breaking changes were introduced. These methods align with the existing service structure and enhance customer account management capabilities.