Handover Praefect sockets on upgrade

In bbcf1e23, the starter package gained HandoverOnUpgrade parameter. Adding the parameter, I missed that Praefect also is using it, and compiles fine without adding the parameter to the struct literals. This means Praefect currently would not handover the sockets during ugprade, which breaks the zero downtime upgrades. This commit fixes the situation by setting Praefect's sockets to be handed over during the upgrades.