Develop the Mock Service

add function

The mock service will interact with an in-memory customary database to save the data. This will be consumed by the mock user interface. We have a list of ItemDto with every new topic one instance of ItemDto that has an item and feature name is added to the list. A Singleton design pattern using enum is charted for the in-memory store implementation. The identifier field starts at one and progresses by one for every new count.