GitHub registry

[PhilWun]

This PR

• replaces Docker Hub with the GitHub registry in the GitHub workflow and updates the used GitHub actions
• makes the image buildable for the ARM architecture

Needed for OpenTOSCA/opentosca-docker#57

[wederbn]

Why exactly do we need this?

[PhilWun]

The Dockerfile tries to install the newest version of bundler which is incompatible with some other dependencies, that's why we have to change the Dockerfile to install the newest compatible version which is 2.3.26 to fix this error:

ERROR:  Error installing bundler:
The last version of bundler (>= 0) to support your Ruby & RubyGems was 2.3.26. Try installing it with `gem install bundler -v 2.3.26`
bundler requires Ruby version >= 2.6.0. The current ruby version is 2.3.0.

[wederbn]

But why using this diff file instead of directly adding it to the Dockerfile?

[PhilWun]

Because the Dockerfile is downloaded from their repository and this way we don't have to worry about the license.

[wederbn]

Can´t we use another image as builder then? Looks like a very hacky solution atm

[PhilWun]

I haven't found another image with Apache Buildr and Jruby. I think the cleanest solution would be to include the Dockerfile after all with the modification and the appropriate license statement.

[wederbn]

LGTM