Migrate from Travis CI to GitHub Actions

[twolfson]

Travis CI was our primary CI tool when developing this repo as well as many others.

However, it's become less friendly to use (e.g. limit on credits) and GitHub Actions is significantly friendlier at CD time (e.g. no credential juggling, part of repo)

As a result, since this repo can be a boilerplate for other servers, it's a good candidate to migrate to GitHub Actions