assignment should not overwrite ticket metadata during backfill

[dzmitry-lahoda]

Is your feature request related to a problem? Please describe. I use ticket for metadata storage (Extensions field). When ticket gets assignment via back, it lost is metadata field. I put metadata from back fill into assignment. But I want ticket metadata in Extensions still to be retained, if it is not overwritten by Extensions from Assignment.

Describe the solution you'd like

1. Create ACK with Assignment and ACK.
2. Get ticket after Assignment. Expected: All Extensions of ticket retained Actual: Ticket looses its metadata in Extensions.

Describe alternatives you've considered Use some other storage to store ticket metadata.

Additional context I assume assignment should not clear metadata.