Add support for Docker labels

Open username-removed-536588 requested to merge jjacobson/gitlab-ci-multi-runner:master into master

What does this MR do?

Adds support for Docker labels.

Why was this MR needed?

For users of Rancher, it is useful to add custom labels to the containers created by the runner. For example, to add a standalone container to the same network as services managed by Rancher, the io.rancher.container.network=true label needs to be added. This allows the container to communicate with the other services on the network, including the Rancher DNS service.

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

To prevent duplicate code, the code to add labels the config has been

Does this MR meet the acceptance criteria?

  • Documentation created/updated
  • Tests
    • Added for this feature/bug
    • All builds are passing
  • Branch has no merge conflicts with master (if you do - rebase it please)

What are the relevant issue numbers?

#1752

Edited by username-removed-536588