Add usage of `LLAMA_STACK_LOG_FILE` to `test-container` CI job

[nathan-weinberg]

#65 was needed to fix an issue with logging in the container job

It's more of a workaround to unblock us, as using the LLAMA_STACK_LOG_FILE functionality in Llama Stack is preferred so we can collect that as a job artifact, similar to what we do with other jobs

This may require some upstream work in Llama Stack