PubSub batching producer improvements

[marcinbudny]

Description

Further changes in pub sub batching producer:

• pass config object instead of parameters to BatchingProducer constructor
• allow to cancel produce of a message by adding a cancellation token
• added configurable retries
• configurable publish timeout
• configurable log throttling
• added batching producer example

Purpose

This pull request is a:

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist

• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)