update dockerfile and add automatic docker build via github actions

[lfoppiano]

This PR:

• updates the Dockerfile using the grobid-full image as a docker base
• update the build so that the config.yaml is read and the grobid-home is correctly used for installing the models
• update the build to support conda environments
• add github actions for automatic build and unit test (now disabled, for when will have them)
• add github actions for manual docker builds with push on docker hub. It's necessary to set up the secrets DOCKERHUB_USERNAME and DOCKERHUB_TOKEN

@kermitt2 I'm wondering whether we should use the CRF models or the DL (as of with this change)?