Feature: Keep synced hero representations up-to-date.

[Tilix4]

Brief description

Keep previously synchronized sites up-to-date by comparing old and new sites and adding old sites if missing in new ones.

Fix #4331

Testing notes:

1. Publish a version from a site A
2. Using the loader, download the hero version
3. Publish the same subset from site B
4. It's being synchronized in site A

[kalisp]

Thanks for contribution :).