stream: Fix sns client name "default" + queue subscription done from sns topics aws account

[applike-ss]

Currently there are two issues with the stream package.

1. The client used for creating the sns topic is always "default". However when we run multiple applications in different accounts, we might want to discover their sns topic, so we need to be able to set the client name via the target.GetClientName().
2. This would lead to another issue we are facing then and that is the way we subscribe something to an sns topic. When the client from the account with the sns topic subscribes something to the topic, there is a subscription notification sent which needs to be confirmed in the destination account. If however we subscribe from the destination account to the source accounts topic, that is not the case.

My suggestion here is to adjust the client name "default" in the stream package to target.GetClientName() and to make the queue subscribe to the topic, not vice versa.