adding auto-register for gitlab-ci-multirruner docker images

This is a general Merge Request template. Consider to choose a template from the list above if it will match your case more.

What does this MR do?

Adds support for autoregister / deregister to alpine docker image.

Why was this MR needed?

In kubernetes world when containers come and go, we need to remove the clutter of registered runners.

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

No.

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?

This pr was requested as an enhancement in PR: https://gitlab.com/charts/charts.gitlab.io/merge_requests/2