Perform docker build and push to DockerHub in GH Actions

[justb4]

Is your feature request related to a problem? Please describe. Builds on Dockerhub are triggered from push to master. These 1) take a long time 2) are not coupled to Travis test result, so broken versions are built and deployed on demo server as well.

Describe the solution you'd like Perform docker build and push to dockerhub in the GHC .travis CI script.

Describe alternatives you've considered Could use commit hooks from GitHub but needs infrastructure (server) and has same disadvantage (not coupled to Travis result).

Additional context

• see https://docs.travis-ci.com/user/docker/
• need to set geopython DockerHub credentials on Travis
• see https://docs.travis-ci.com/user/environment-variables/#defining-variables-in-repository-settings

[justb4]

Another way is to do Docker build in GitHub Actions. This is at least faster.

[justb4]

Will use GH Actions, and later migrate Travis to GH Actions as well.

[justb4]

Finally: via #354 #355 #356 #357 as the final test is when pushed to GH master...Now working:

• on pull-request: build Docker Image and run GHC Unit Tests
• on push to master: ditto but also push latest to DockerHub

Took some fiddling with docker/build-push-action@v2 (use load: true and push: false) and env var manipulations.