Implement a MessageHandler which handles Deposit event Messages

The implementation should be added the skeleton DepositMessageHandler

A deposit needs to be sent to an ExternalSystem, and information must be stored about a deposit for later display to users. Persistence should be done using a DepositPersistence instance. For the purpose of this task, we do not require an implementation of DepositPersistence, just adding the required methods to the interface would suffice.

1. Messages are delivered with at-least-once delivery guarantee.
2. The ExternalSystem is not idempotent, it is a critical need to ensure that a deposit is never sent twice.
3. If you wish to make use of a Transactional Persistence Layer, please make it clear what assumptions are made