If the cli is called from a github action, format output messages accordingly

[garethjevans]

We could add a --output github-actions flag, when this is enabled , use output markers to make the output more acceptable in github actions (https://docs.github.com/en/actions/using-workflows/workflow-commands-for-github-actions) e.g.

• ::debug::message for debug messages
• group log lines together with ::group::{title} & ::endgroup::