This commit includes a Dockerfile for building a test environment for
future CI pipelines. This commit also refactors the GitLab CI pipeline
files by splitting the jobs into different files:
- .gitlab-ci.yml: Global CI pipeline file.
- .gitlab/ci/test-env.gitlab-ci.yml: Jobs to test and publish the
docker image for the test environment.
- .gitlab/ci/playbook.gitlab-ci.yml: Jobs to test and publish the
docker image for the pleroma playbook
- .gitlab/ci/templates/docker.gitlab-ci.yml: Template jobs for
testing and publishing docker images.
Part of dananglin/pleroma-ansible-playbook#17