Generating lazy completion scripts for Bash/Zsh

[segevfiner]

It would be nice to be able to generate lazy loaded completion scripts for Bash and Zsh instead of having to eagerly register and execute them at shell startup by register-python-argcomplete. For Bash, it is likely the existing script can be used as is, for Zsh, you need #compdef <command> as the first line and to not call compdef but rather call the completion function directly, there is probably a trick or two to make the script work as both. I think click-completion uses one https://github.com/click-contrib/click-completion/blob/master/click_completion/zsh.j2, and also cobra https://github.com/spf13/cobra/blob/main/zsh_completions.go, but there are also others, not sure which is the best.

[kislyuk]

Yes, that would be nice. PRs are welcome.