Merge branch 'add-docker-image-template' into 'master'

Add a template to build docker images, which is copied from . The idea is that those repositories can refer to the template rather than duplicating the same steps.

This also adds a minimal linting for the yaml files so that we at least get feedback of obviously broken files. Later we want to improve on that.

See merge request !1
1 job for master in 26 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Verify
passed #63
docker-alpine
lint

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