Add tab completion to dfx

[bitdivine]

Motivation

When writing commands, tab completion helps.

Proposed implementation

clap generates tab completion scripts. Can we use it please?

An example of how tab completion is installed in another project: https://rust-lang.github.io/rustup/installation/index.html#enable-tab-completion-for-bash-fish-zsh-or-powershell

• Clap tab completion: https://docs.rs/clap_complete/latest/clap_complete/
• Docs: https://docs.rs/clap_complete/latest/clap_complete/index.html
• Proposed usage:
  • Note: The clap example uses the subcommand generate but dfx already uses that for other purposes.
  • Installing tab completion explicitly:
  • dfx completions bash > /usr/share/bash-completion/completions/dkg
  • .. and similar for other shells
  • Tab completion could be installed automatically when dkg is installed.

[sesi200]

This is part of our roadmap and will be implemented at some point (hopefully not too far out...).

[ukaznil]

I'm tackling on it now. For tentative use, you can refer to my samples: https://github.com/ukaznil/dfx-completions Later on, I will think which options we can take to integrate it with this sdk repo.