Close deleted subscriptions

Today, the subscription manager in Notification service doesn't close/unregister deleted subscriptions for SB topics. In a scenario when a subscription is deleted, the registered client still attempts to pull messages from the subscription (which doesn't exist now).

This causes an explosion of error logs in the Trace table. The log message looks like this: Exception RECEIVE occurred in service bus message in exception phase The messaging entity '<service-bus-resource>:topic:recordstopic~15|<notification-id>' could not be found

The number of such logs is very very large, they only go away when service is restarted.

This solution closes the connections for which the subscription doesn't exist in the cosmosDb