cannot deploy openmldb with one tablet configured

[gaoboal]

Bug Description
When deploying OpenMLDB, I commented out one tablet entry in the hosts file, then executed deploy-all.sh and start-all.sh to deploy OpenMLDB. However, the startup failed with the following error in logs/nameserver.INFO:
E20240412 16:06:11.900566 22976 name_server_impl.cc:5549] tablet num 1 is less than system table replica num 2

Expected Behavior
Should be able to configure only 1 tablet and deploy successfully

Steps to Reproduce

1. edit conf/hosts:

[tablet]
172.27.234.11:30921 /tmp/openmldb/tablet-01
#172.27.234.11:30922 /tmp/openmldb/tablet-02
[nameserver]
172.27.234.11:37527
[apiserver]
172.27.234.11:9080
[taskmanager]
172.27.234.11:9902
[zookeeper]
172.27.234.11:32181:2888:3888 /tmp/openmldb/zk-1

2. execute sbin/deploy-all.sh and sbin/start-all.sh