Create custom images for SLO checker

We experienced immense memory usage of our SLO checkers. Combined with resource constraints on the memory, OOM and killed processes can be observed.

This might be causes by this issue: https://github.com/encode/uvicorn/issues/1226

As uvicorn-gunicorn-fastapi-docker also reports:

🚨 WARNING: You Probably Don't Need this Docker Image

You are probably using Kubernetes or similar tools. In that case, you probably don't need this image (or any other similar base image). You are probably better off building a Docker image from scratch as explained in the docs for FastAPI in Containers - Docker: Build a Docker Image for FastAPI.

we should simply build the image on our own.