How do I add new autocompletions to the autocomplete dropdown?

### Checks

- [x] I have searched [github.com/aws/amazon-q-developer-cli/issues](https://github.com/aws/amazon-q-developer-cli/issues?q=) and there are no duplicates of my issue

### Operating system

macOS 15.5.0 (24F74)

### Expected behaviour

With fig, you used to be able to contribute [custom completion specs](https://fig.io/docs/getting-started/first-completion-spec).

### Actual behaviour

It's no longer clear how to do that.

### Steps to reproduce

_No response_