Cart initialization logic on app load

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Cart initialization logic on app load
In order to make any real card work in requires some initialization logic (creating the cart or laoding the existing cart, ...). This should be handled by the cart ComponentStore

Describe the solution you'd like
For Spree url-storefront SDK the cart should be created once application has been initialized (take a look at the Spree API Endpoint)

Once the user sessions are implemented we should prior to above perform the User's Cart retrieval (take a look at the Spree API Endpoint and only if its not available create the new one (as mentioned above).

This should all be implemented within the Spree SDK wrapper (since its custom to 3rd Party Providers) and use within the Cart ComponentStore (indirectly through main StoreSDK service method).