Restore mirror step in CI pipeline

Closed Tomasz Maczukin requested to merge feature/restore-mirror-step-in-pipeline into master

What does this MR do?

(Re)adds a mirror step to CI pipeline. The step is pushing a master branch or a tag to github.com:ayufan/gitlab-ci-multi-runner.

Why was this MR needed?

This is needed - for example - to execute automatic builds on hub.docker.com, which are synchronized with changes in the github repository.

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

Does this MR meet the acceptance criteria?

  • Branch has no merge conflicts with master (if you do - rebase it please)

What are the relevant issue numbers?

Closes #1713 (closed)

/cc @ayufan