feat(ci): Add functionality to disable pushing image to dockerhub

[PythonGermany]

Summary

Adds functionality to disable publishing image to dockerhub for all workflows in the repository by setting action variable DISABLE_DOCKERHUB_PUBLISH to true in repository settings.

I will be using this in my fork to be able to use all relevant workflows without having to setup dockerhub credentials.

Checklist

• Tested and/or added tests to validate that the changes work as intended, if applicable.
  • I tested if the new functionality I need works
• I am not able to verify if the default behavior (publish to both ghcr and dockerhub) is still functional as expected because I have no dockerhub credentials to test it with. If there is interest to merge this I'd appreciate it if someone else could verify that the default behaviour is not broken
• (n/a) Updated documentation in README.md, if applicable.

[PythonGermany]

This part of the new implementation needs to be tested by someone who has dockerhub credentials set up in their fork.