Pubsub message encoding performance could be improved?

[daspecster]

See: #2773

I'm not sure on the data size limits for pubsub, but if they're significantly large then there are probably more performant message encoding strategies that could be implemented.

[daspecster]

Per #2773 (comment) and https://cloud.google.com/pubsub/quotas

Publish request	Total size must be no more than 10MB .
Must contain no more than 1,000 messages.

Message	The maximum number of attributes per message is 100.
The maximum size of an attribute key is 256 bytes.
The maximum size of an attribute value is 1024 bytes.

[danoscarmike]

Batching code is an elegant solution and is already in master and latest release