Motivation

The google pubsub client allows you to configure your receive and publish settings. via pubsub.ReceiveSettings and pubsub.PublishSettings. This sdk exposes the ReceiveSettings in its interface via the protocol Struct but does not give the same treatment to PublishSettings. I propose we correct this omission with a backwards compatible change exposing this and thus allowing the user to configure things like batch publishing of messages without effecting the existing behaviour of the client.

As PublishSettings are not currently configurable, all events are published with pubsub.DefaultPublishSettings. This means that even by exposing ReceiveSettings we would not impact any programs which rely upon not specifying PublishSettings.