[Example] Add cross-account bank transfers

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In the "bank account" example add a cross account transfer to show how the transaction itself can be backed by an event stream and that can be acted on as a form of saga.

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This could also demonstrate the idea of the causation identifier which would link the source withdrawal and the target deposit to the transfer command identifier.

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Events:-

• Transfer initiated
• Source funds withdrawn
• Target funds deposited
• Refund initiated
• Source funds refunded
• Refund failed

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Projections:-

• Transfer State (Initiated -> Funded -> Transferred / Transfer Failed -> Refunded -> Refund failed)

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Classifications:-

• Failed refunds (these might require manual intervention)

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Commands:-

• Transfer money
• Cancel in-progress transfer

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Queries:-

• GetTransferState - Get the current state from the "Transfer State" projection