[BUG] Use container image if present for testing

[duncdrum]

We can streamline the CI config by using the container config, if the user decided to create one during the prompt phase.

This should provide results closer to the production config, and make the config files less verbose

[duncdrum]

we'd loose the ability for forward testing, and without processing secrets as part of the prompt phase we shouldn't include deploy instructions beyond the inline that are already there.

So this won't be happening anytime soon.