[Docs] Update Migration Docs

[6543]

• Migrate reviews when migrating repository from github Migrate reviews when migrating repository from github #9463
• Migrate reactions when migrating repository from github Migrate reactions when migrating repository from github #9599

both need to be added to https://docs.gitea.io/en-us/migrations-interfaces/

[bagasme]

@6543 rough guides?

[6543]

Mostly update Downloader Interfaces and Uploader Interface