Returns the state of a clone operation: its status, the ids created so far and the status, attempts and last error of each step.

Needs an admin session (API users are refused), the multi-retailer-login flag active for the caller's retailer, and a caller whose retailer is the MAIN contract of a group. Unlike the create route, it does not check the store-clone flag, so an operation can still be read while the flag is off.

An operation that belongs to another group answers 404, the same as an operation that does not exist, and never 403. This is on purpose: it stops a caller from finding out which operation ids exist in other groups.