RATIS-1430. Add ratis-shell addPeer command

[codings-dan]

What changes were proposed in this pull request?

Add a sub command to add peer.

What is the link to the Apache JIRA

https://issues.apache.org/jira/browse/RATIS-1430

How was this patch tested?

[~/local/myproject/ratis] [addPeer *] -> %  mvn clean install  assembly:single -DskipTests -Dmaven.javadoc.skip=true -Dlicense.skip=true  -Dfindbugs.skip=true -Denforcer.skip=true -Dgpg.skip=true   -Djsse.enableSNIExtension=false  -Prelease -Papache-release
[~/local/myproject/ratis] [addPeer *]-> % cd ratis-assembly/target
[~/local/myproject/ratis/ratis-assembly/target] [addPeer *] -> % tar -xzf apache-ratis-2.3.0-SNAPSHOT-ratis-shell.tar.gz
[~/local/myproject/ratis/ratis-assembly/target] [addPeer *] -> % cd apache-ratis-2.3.0-SNAPSHOT
[~/local/myproject/ratis/ratis-assembly/target/apache-ratis-2.3.0-SNAPSHOT] [addPeer *]-> % bin/ratis sh info -peers localhost:19200,localhost:19201
group id: 02511d47-d67c-49a3-9011-abb3109a44c1
leader info: localhost_19200(localhost:19200)

[server {
  id: "localhost_19200"
  address: "localhost:19200"
}
commitIndex: 12
, server {
  id: "localhost_19201"
  address: "localhost:19201"
}
commitIndex: 12
]
[~/local/myproject/ratis/ratis-assembly/target/apache-ratis-2.3.0-SNAPSHOT] [addPeer *]-> % bin/ratis sh quorumAdd -peers localhost:19200,localhost:19201 -addPeer localhost:19202
 [~/local/myproject/ratis/ratis-assembly/target/apache-ratis-2.3.0-SNAPSHOT] [addPeer *]-> % bin/ratis sh info -peers localhost:19200,localhost:19201,localhost:19202
group id: 02511d47-d67c-49a3-9011-abb3109a44c1
leader info: localhost_19200(localhost:19200)

[server {
  id: "localhost_19200"
  address: "localhost:19200"
}
commitIndex: 12
, server {
  id: "localhost_19201"
  address: "localhost:19201"
}
commitIndex: 12
, server {
  id: "localhost_19202"
  address: "localhost:19202"
}
commitIndex: 8
]

[codings-dan]

This work has been completed in #534 , so close.