Add gotData and endOfProcess handlers

[velom]

Summary

Add two new handlers to track the processing:

1. Helper WithGotData allows to pass a function will be triggered on every processing data block.
2. Helper WithEndOfProcess allows to pass a function will be triggered when the whole processing going to be finished.

Checklist

Delete items not relevant to your PR:

• [x] Unit and integration tests covering the common scenarios were added
• [x] A human-readable description of the changes was provided to include in CHANGELOG

[CLAassistant]

All committers have signed the CLA.