Add push_type argument for client.send_notification

[namrata93]

Add a push_type argument to client.send_notification. Currently I have to make use of the code to deduce the push_type from the topic, which is forcing me to create a topic when I think it's easier to just pass in the push_type

This argument is already present in the method client.send_notification_batch so simply mimicking it.

[Pr0Ger]

Hi

Thanks for contribution! Can you fix indentation to not use mixed tab/spaces?