Add EventMesh CLI

[simpleidserver]

Support the following commands eventmeshctl:

Commands

• `help -l | --list-commands : list command usages only.
• help command_name : print usage for the specified command.
• version : Display CLI tools version.
• stop : stop the EventMesh node.
• cluster_status : display all the nodes in the cluster.
• add_vpn : add a vpn.
• add_client : add a client.

Options

• -n : default node is localhost:4000.