[Docs] Document API change for `Query::REST`

[d0cd]

📚 Documentation

This PR, explicitly introduces versioning to the Query::REST variant. Prior to this, this variant was initialized in Leo with the full API: https://api.explorer.provable.com/v1. It must now be initialized as https://api.explorer.provable.com and version selection is no longer possible.

[kaimast]

#3001 adds version detection to the RestQuery logic. This change should resolve problems where users add the version to the URL explicitly.