Use Case: As a seller, I want to set delivery price for the buyer

[yg-apaza]

• [x] Add entity tests: shouldEmitEventWhenSettingDeliveryPrice, shouldForbidSettingDeliveryPriceByNonSeller
• [x] Add service test: shouldSetDeliveryPrice
• [x] Update TransactionEntity and add service call ServiceCall<Integer, Done> setDeliveryPrice(UUID itemId)
• [x] UI: transaction.scala.html will show a button "Set delivery price" if the current user is the seller and it will redirect to form for submit the delivery price