Provide an automatic migration of CLI prototype files to the new version 3 format.
Probably as a command of the version 3 CLI, or could be a separate script or npm module.
Timebox the effort to 2 days of work, if it would take more time then we will not provide automated migration and will simply document how to do the migration manually.

Consider that developers might have customized prototypes in the globally installed CLI (though not recommended), and they may have customized prototypes in any location that they have previously run the customize-local-config command.

Reason: Any customized prototypes will no longer work once a user upgrades to version 3.