Autobuild Docker images and push to GitHub Container registry using GitHub Actions

[anthonyfok]

In light of Changes to Docker Hub Autobuilds, our team has decided to autobuild our Docker images (opendrr/python-env and opendrr/pygeoapi) and push them to GitHub Container registry.

Tasks

• [x] Build and push to https://ghcr.io/opendrr/pygeoapi
  • Sorry, I didn't do a PR
  • See https://github.com/OpenDRR/pygeoapi/compare/master~2...v0.10.1.gsc20211013.1 for the changes (see smaller incremental changes in my fork: https://github.com/anthonyfok/pygeoapi/compare/anthonyfok-ghcr-hub-tests~5...anthonyfok:anthonyfok-ghcr-hub-tests)
• [x] Build and push to https://ghcr.io/opendrr/python-env
  • [x] OpenDRR/python-env#1
  • [x] OpenDRR/python-env#2
• [x] OpenDRR/opendrr-api#133 Update pygeoapi/Dockerfile and python/Dockerfile at https://github.com/OpenDRR/opendrr-api to use the ghcr.io registry, i.e. use FROM ghcr.io/opendrr/pygeoapi and FROM ghcr.io/opendrr/python-env
• [ ] Document what changes I made that differ from https://github.com/metcalfc/docker-action-examples/blob/main/.github/workflows/main-ci.yml and explain why