Completion subcommand for kubectl-moco

[ymmt2005]

What

This is not possible for the time being. ref: https://github.com/kubernetes/kubernetes/pull/105867

spf13/cobra can auto-generate shell completion rules, so add completion subcommand to kubectl-moco for Bash, Zsh, PowerShell, Fish, etc.

Note that it should work when invoked as kubectl moco ....

How

Describe how to address the issue.

Checklist

• [ ] Finish implementation of the issue
• [ ] Test all functions
• [ ] Have enough logs to trace activities
• [ ] Notify developers of necessary actions

[ymmt2005]

@masa213f @d-kuro looks like k8s 1.26 will support completion for kubectl plugins. https://qiita.com/superbrothers/items/65a16f5139b52e1b9d56