feat: move alias and completion scripts into binary

[natescherer]

Hello again! 😊

So as I was thinking about what would be needed to get this working with Windows, I realized that adding alias and completion scripts for PowerShell was going to be necessary. That got me thinking: how would you feel about moving the alias and completion scripts into the binary itself, similar to how Starship does it?

My thought was the existing scripts get rolled into commands that get added to the shell init files like this:

Bash

eval "$(kubesess init bash)"

Fish

kubesess init fish | source

PowerShell

Invoke-Expression (&kubesess init powershell)

Zsh

eval "$(kubesess init zsh)"

If you're amenable to this design change, I'll draw up a PR to refactor the current Bash/Fish/Zsh setup to use this method and then design the Windows/PowerShell compatibility to use it as well.

This would potentially make it easier to add this as a Krew plugin too, as, at that point, you'd just have a single binary to deal with.