[cli] Tab completion for zsh / tcsh / fish

**Describe the bug**
Tab completion on Ubuntu only works for bash.

**To Reproduce**
How, and what happened?
1. `zsh`
1. `multipass `
1. lists directory contents

**Expected behavior**
show commands like for bash

I would suggest adding completion scripts for zsh, tcsh and fish.
https://snapcraft.io/docs/tab-completion suggests this is possible referencing https://github.com/snapcore/snapd/blob/master/data/completion/bash/complete.sh

Start by locating the existing bash completion implementation in Multipass and compare it with the snapd completion example linked in the issue. Add equivalent completion scripts for zsh, tcsh, and fish, then verify that typing `multipass ` shows commands rather than directory contents in each shell.

Written by the indexing model from the issue text.