Dockerhub Repository for Blueprint

[jfaltermeier]

Currently we are using this dockerhub user https://hub.docker.com/u/eclipsetheia to publish an image we are using for building Theia Blueprint: https://hub.docker.com/r/eclipsetheia/theia-blueprint

I would like to publish the built docker image of Theia Blueprint itself as well. I've setup a workflow here: https://github.com/eclipse-theia/theia-blueprint/blob/master/.github/workflows/publish-blueprint-img.yml This tries to publish this as eclipsetheia/blueprint:1.35.0 (version can be specified) and eclipsetheia/blueprint:latest

For this to work we have to create the blueprint repository in https://hub.docker.com/u/eclipsetheia first