feat: enhance plugin networking capabilities support IPV6

[appleboy]

• Enable SSH server to listen on all interfaces by uncommenting relevant lines in sshd_config
• Add new protocol and proxy.protocol flags to main.go with usage information and default values
• Change the Port field type from string to int in plugin.go and plugin_test.go
• Refactor variable name from host to h and add port variable in plugin.go loop
• Remove commented-out code and refactor hostPort function in plugin.go
• Add import for io package in plugin_test.go
• Add new test function TestPlugin_hostPort with multiple test cases in plugin_test.go