[OpenSign] Provide an official Docker image on Docker Hub

### Feature Title Official Docker Image ### Feature Description Currently everywhere in your project you tell people to build the binary themselves, and thus build the docker image themselves too. It's obvious that this comes from a place of transparency/security, and that's good. However, all major projects SHOULD provide an official Docker image on the docker hub (or another trusted public registry). ## 1st Without any docker images, this means every user must build the program all the time. Ecologically, this is a huge waste of resources when there's only need for one person building the image, then making it available online (like for all major open source projects and distribution packages). ### 2nd This makes everyone not wanting to build themselves lose time for nothing (if someone doesn't trust your official docker image, I would gladly like to get their answer on if they did vet your whole source code). ### 3rd and the most important: Not doing so, y