Find alternative to Travis CI for deploying images

[biggianteye]

This repo used Travic CI for building and testing images as well as pushing them to docker hub. According to the banner there:

Since June 15th, 2021, the building on travis-ci.org is ceased.

The most recent build of images currently available are from April 21st 2021. An alternative needs to be found for the built/test/deploy processes. github actions might be a good candidate, but other options are also feasible.

[biggianteye]

In the meantime, a member of the graze team can manually build and push images (eg. make build-8.0 tag-8.0 test-8.0 push-8.0). I've just done this for 7.1, 7.2, 7.4, 7.4 and 8.0.