Change creator_id to only need to be unique for schools where rejecte…#742

jamiebenstead merged 6 commits intomainRaspberryPiFoundation/editor-api:mainfrom

1233-creators-of-previously-rejected-schools-cant-sign-upRaspberryPiFoundation/editor-api:1233-creators-of-previously-rejected-schools-cant-sign-upCopy head branch name to clipboard