feat: Support taking screenshot when test fails

[k-ane]

Not sure if this is currently possible or maybe related to #197.

But would love to be able to pass an option to fluttium.yaml to allow taking screenshots on test failure.

What I'm hoping to do is run in CI and get screenshots of the failed tests and well as the logs, to save as artifacts and send to Slack maybe.

[wolfenrain]

That should be doable once I land !293, with that refactor we have more control over what we want to do once a test fails for instance.

Thanks for opening up this feature request! It is a solid one