Introduces transaction support.
Operations can now be executed inside a TransactionScope providing atomicity.
Supported operations for transactions:
`SendAsync`, `CompleteAsync`, `DeferAsync`, `DeadLetterAsync`, `AbandonAsync`
Transaction cannot work across connections. Hence, to be able to Send and Receive in a single transaction, `ServiceBusConnection` object has been exposed. Each of the client entities now accepts an already created connection.
Sample usage:
```csharp
var connection = new ServiceBusConnection(ConnectionString);
var sender = new MessageSender(connection, QueueName);
var receiver = new MessageReceiver(connection, QueueName);
var receivedMessage = await receiver.ReceiveAsync();
using (var ts = new TransactionScope(TransactionScopeAsyncFlowOption.Enabled))
{
await receiver.CompleteAsync(receivedMessage.SystemProperties.LockToken);
await sender.SendAsync(message).ConfigureAwait(false);
ts.Complete();
// Or, ts.Dispose();
}
await sender.CloseAsync();
await receiver.CloseAsync();
await connection.CloseAsync();
```
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