Build using Github Actions

[manios]

Up to that point, we tried to use both Dockerhub automated builds and Travis CI in order to build our image. However, we encountered the following problems:

• Our image is being built for multiple architectures (x86, amd64, arm/v6, arm/v7 ) using QEMU and the total build time can be over 60 minutes. Dockerhub and Travis CI builds throw a timeout on 60 minutes and the build stops.
• Dockerhub does not support experimental features at all, such as docker manifest and docker buildx, (at least until the time of writing this issue)
• Dockerhub does have a terrible community support. Check the issues in docker/hub-feedback Github project.

Due to the aforementioned issues, we chose to use Github Actions in order to build our multi-platform image. Github Actions provide us with:

• Less restrictive time limits: Max job time is 6h according to the current Usage Limits.
• Official support for multi-platform Docker builds with QEMU using Docker Setup QEMU action.
• Official support for docker buildx using Docker Setup Buildx action.
• Official support for caching layers in multi-stage builds using actions/cache action.