Move docker image to dockerhub

Currently we are publishing docker images for this package to the github container registry `ghcr.io`. We are already paying for dockerhub, I think, so maybe it makes sense to move there?

To implement this, we would update the [build-docker](https://github.com/AlexsLemonade/scpcaTools/blob/main/.github/workflows/build-docker.yaml) action to point to dockerhub. I believe we would also need to update secrets for this repo to access the credentials for dockerhub.

Start by reading .github/workflows/build-docker.yaml to trace how the image is currently published to ghcr.io. Check which repository secrets are available and what Docker Hub credentials the workflow would need. Done means the workflow publishes the package image to Docker Hub instead of ghcr.io.

Written by the indexing model from the issue text.