[feat] Dynamic Bash/Fish tab completion for CLI

[GarthDB]

Is your feature request related to a problem? Please describe.

It can be tricky to remember all package names and tasks when using the CLI. This results in me digging through files or trying to guess.

Describe the solution you'd like

A tab completion function, similar to this git-completion.bash script that would dynamically use the data in moon.yml files.

Describe alternatives you've considered

I'm not sure there is an alternative.

Additional context

If this already exists I was having a hard time finding it, so maybe I'm using the wrong keywords.

[milesj]

@GarthDB We have moon completions but that's just for the built-in commands. I'm assuming you want it to also auto-complete all the available tasks/projects/etc? If so, it's blocked on this currently (unless we build our own engine): clap-rs/clap#3166