When the daemon is started with `--hardfork-handling migrate-exit` and the
necessary hard fork config has been set (the two stop slots and the
`hard_fork_genesis_slot_delta`), the daemon will now automatically save a Mesa
hard fork configuration in `auto-fork-config-{network_id}`. The `network_id`
will be `mainnet`, `devnet`, or `other-network-{name}`, depending on the
compile-time and runtime config for `daemon.network_id`.
