Add Github Actions

[gravesm]

This is an initial attempt at setting up Github Actions. It's not
optimal, but it does the job until I can figure out better ways to do
things. The biggest issue is that I think the tests workflow should
probably be turned into an action since it's reused in both the test and
deploy workflows.

On push the usual CI jobs will run. On merging into master the CI jobs
will run and then, if successful, a new image for the workflow container
will be built and deployed. The staging Airflow cluster will be
redeployed with the new image.

How can a reviewer see these changes?

Marvel at the Actions tab on the repo.

Reviewer Checklist

• The commit message is clear and follows our guidelines
• There are tests covering any new functionality
• The documentation has been updated if necessary
• The changes, if applicable, have been verified

[JPrevost]

This PR adds GitHub Actions but does not remove the Travis CI stuff. I approved with the assumption you'll pull that out soon in a separate PR.

[JPrevost]

Are you sure we want to checkout master here? I'm still unclear on the configs so I may be missing things, but it feels like this would always checkout the master branch even on push to another branch?

[gravesm]

I know it looks like I'm checking out the master branch, but that's not what's happening. What that line does is use the master branch of the checkout action. It will checkout whatever version of the codebase triggered the workflow. There's a little more info here: https://github.com/actions/checkout#usage.

[JPrevost]

Same question here as the other... not sure if I don't understand or if this should be modified.

[gravesm]

I debated removing the travis config on this PR. I think I'm inclined to leave it in for another PR or two to make sure the actions are doing what I think they're doing. But yeah, my plan is to get rid of travis.