Investigate: extraction of the pull mirroring from the import process

Part of the epic: &8685

We have two mirror implementations:

1. Pull mirror
2. Push mirror

The push mirror is a separate entity based on RemoteMirror class.

The pull mirror is a part of the import process. This leads to multiple if mirror? verifications in the code to distinguish between Import and Pull Mirroring flows.

Proposal

Extract the pull mirroring code from the import flow. It should have a positive effect on readability.