Automate docker build with github actions

[jennyfothergill]

Pushing 3gb images to docker hub is hard on my internet. This way we can automatically build and push the container. See https://github.com/docker/build-push-action and https://docs.github.com/en/actions/reference/workflow-syntax-for-github-actions#onpushpull_requestpaths for more info

[codecov[bot]]

Codecov Report

Merging #34 (c82bec3) into master (743021b) will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #34   +/-   ##
=======================================
  Coverage   98.76%   98.76%           
=======================================
  Files           6        6           
  Lines         162      162           
=======================================
  Hits          160      160           
  Misses          2        2