Use the `completions_options` config throughout

[dalmaer]

completions_options is used inside query.html but not in areas such as:

ask_embeddings.py:

    # Borrowed from https://github.com/openai/openai-cookbook/blob/838f000935d9df03e75e181cbcea2e306850794b/examples/Question_answering_using_embeddings.ipynb

    prompt = f"Answer the question as truthfully as possible using the provided context, and if the answer is not contained within the text below, say \"I don't know.\"\n\nContext:\n{context} \n\nQuestion:\n{query}\n\nAnswer:"
    return get_completion(prompt, answer_length=answer_length, completion_model=completion_model)```