gcli command auto completion and arm64 build

- Extra command `completion` added which takes a `--shell` argument to generate a completions script for a specified shell.
- Adapted the Linux (amd64) build to:
  - generate the `gcli-completion.bash`, `gcli-completion.zsh`, `gcli-completion.fish`, `gcli-completion.ps1` completion scripts
  - add the `bash`, `zsh` and `fish` completion scripts in the `.deb` package
- Added the ARM64 build generating a binary and a `.deb` package that also include those completion scripts.