Added acknowledgement for pub/sub Streamer

[Saikat Maitra]

Hi Emmanouil,

I have reviewed and merged changes for following jira issue.

Jira : https://issues.apache.org/jira/browse/IGNITE-12645
PR : https://github.com/apache/ignite-extensions/pull/8

Thank you for your contribution.

Regards,
Saikat