Operations: Add background operations support to entity hub

[iLLiCiTiT]

Changelog Description

Implemented background operations methods and use it in entity hub.

Testing notes:

1. Try to use send_background_batch_operations and get_background_operations_status.
2. Result of send_* should do the same as send_batch_operations. And get_* should return the info about it.
3. Using EntityHub should still work as before (or better).