Add shell completions for Killgrave CLI

[joanlopez]

Based on the most recent changes present on the branch v0.5.0, it seems Killgrave is introducing the use of Cobra as the library used to build and run the CLI commands.

Thus would be good to also add the shell (Bash, Zsh, fish, PowerShell) completions supported by the library.
More information here.

[MayukhSobo]

@joanlopez The document link is not working!

[joanlopez]

Looks like now it's under https://github.com/spf13/cobra/blob/main/site/content/completions/_index.md
Are you planning to work on this? @MayukhSobo

[MayukhSobo]

@joanlopez Yes I would be happy to work on it. Can you assign this to me?