feat(join): check cluster conditions before join
chore(config): move Sanitize and Force check to boot process

Make Load function just load parameters. So etcd instance could
use Config struct to start service.
tests(snapshot): expand reasonable range for index

snapshot file was createed with name '0_1010.ss' when testing.
refactor(tests/server_utils): use etcd instance

Remove duplicated etcd start code.
refactor(etcd): expose more peer server start logic

Move closer to the framework with standby logic
fix(server): reload cluster config when reboot
hehe
feat: implement standby mode