Warp sync part II (#9284)

* Gap sync

* Gap epoch test

* Simplified network requests

* Update client/db/src/utils.rs

Co-authored-by: cheme <[email protected]>

* Fixed v1 migration and added some comments

* Next epoch is always regular

* Removed fork tree change

* Apply suggestions from code review

Co-authored-by: Bastian Köcher <[email protected]>

* Added a comment and converted assert to error

Co-authored-by: cheme <[email protected]>
Co-authored-by: Bastian Köcher <[email protected]>