STORY: As a developer testing LLM prompt changes, I want an override option in the docker-compose, so that I can easily change the prompt without rebuilding containers.

[jeffbl]

Right now, LLM prompts are hard coded in various containers, including text-followup, content-categoriser, and graphic-caption. This is good, and should be kept, since it means they are versioned in git. However, to change the prompt, the container must be rebuilt. This work item is to have an environment variable [PREPROCESSOR_NAME]_PROMPT_OVERRIDE that can be set to replace the hard-coded prompt.

Note this may also be of use to someone deploying an IMAGE server, and using another LLM that requires tweaks to the prompt. They would also be able to avoid rebuilding the container, and just make their change in the docker-compose.