autocompletion should list stages by appearance order in the tutorial

the autocompletion returns the list of stages to break at sorted by alphabetical order:

```
└──╼> markdown-runner docs/tutorials/prometheus_locked_down.md --break-at
certs deploy grafana init messaging scrape teardown test_setup verify
```

Which is not practical to know where to stop if you're aiming for the previous to the last one for instance.

Run the shown markdown-runner command and trace the --break-at autocompletion entry point. Compare its current alphabetical output with the stage order in docs/tutorials/prometheus_locked_down.md; done means the suggestions follow their appearance order so users can identify the preceding stage.

Written by the indexing model from the issue text.