Docker images for ARM

Looking for a runner for ARM devices a while ago just found the binaries but no docker image, so based on the alpine runner for amd64 Dockerfiles decided to build one for ARM, been using it for a couple of weeks, here's the repository.

What does this MR do?

• Prosposal for ARM docker runner based on the amd64 alpine Dockerfile.

Why was this MR needed?

• Because there is no official docker image for ARM available.

Are there points in the code the reviewer needs to double check?

Since the image needs dumb-init in order to work, but it is not officially compiled for ARM, this is built in a separate job within the CI file attached to this MR.

• .gitlab-ci.yml needs to be edited/moved.

Does this MR meet the acceptance criteria?

• Built, tested and currently being used in some personal projects, the pipelines passed
• Documentation created/updated: Pending I've found some problems detecting the docker socket, wrote a usage guide , which includes a trobleshooting for the socket detection as well.
• Tests
  • Added for this feature/bug
  • All builds are passing
• Branch has no merge conflicts with master

What are the relevant issue numbers?

#2076