Add support for gitlab-runner-docker-cleanup

When running the runners for some time, some of my nodes get their /var/lib/docker/overlay2 folders absolutely filled with subdirectories. They proceed to behave strangely and not schedule any more runner jobs.

I believe this is related with this https://blog.cloud66.com/docker-with-overlayfs-first-impression/, mentioned in https://gitlab.com/gitlab-org/gitlab-runner-docker-cleanup.

For now I'm running these cleanup containers directly on the nodes (hopefully they'll fix this issue), but shouldn't this cleanup container be ran as part of this chart? Probably as a DaemonSet?