provide stitch cli via docker

[lukasalexanderweber]

I'm just learning docker and thought the stitching package, especially its CLI, is a good example of how to create an image and run it as a container while using a volume to access user data.

To-Dos

• [x] setup a Dockerfile which builds and installs the stitching package into a docker image
• [x] push a test image on Dockerhub -> https://hub.docker.com/r/openstitching/stitch
• [x] document in the Readme how to use the Image
• [x] set up github action to build and push a new Image if a new stitching version is released
• [x] provide a latest tag?