Renamed "PositionAwareSubscriptionModel" to NonDurableSubscriptionModel?

[johanhaleby]

Maybe that would be more intuitive than PositionAwareSubscriptionModel? So instead of:

// Create the non-durable subscription instance 
PositionAwareSubscriptionModel nonDurableSubscriptionModel = ...
// Create the storage
SubscriptionPositionStorage storage = ...

// Now combine the non-durable subscription and the subscription position storage
SubscriptionModel durableSubscriptionModel = 
                  new DurableSubscriptionModel(nonDurableSubscriptionModel, storage);

// Start a subscription
durableSubscriptionModel.subscribe(
                         "mySubscriptionId", 
                         cloudEvent -> doSomethingWithTheCloudEvent(cloudEvent)
); 

we would have:

// Create the non-durable subscription instance 
NonDurableSubscriptionModel nonDurableSubscriptionModel = ...
// Create the storage
SubscriptionPositionStorage storage = ...

// Now combine the non-durable subscription and the subscription position storage
SubscriptionModel durableSubscriptionModel = 
                  new DurableSubscriptionModel(nonDurableSubscriptionModel, storage);

// Start a subscription
durableSubscriptionModel.subscribe(
                         "mySubscriptionId", 
                         cloudEvent -> doSomethingWithTheCloudEvent(cloudEvent)
); 

Alternatlivey: TransientSubscriptionModel.

Think about how we would support some DB that holds the checkpoint as a part of the user? Then it is a DurableSubscriptionModel, but it can't use the same class (but we could create an interface though) since it takes an instead of SubscriptionPositionStorage.