Make the `gitlab-runner register` command happen in a single operation
Description
Make the gitlab-runner register command happen in a single operation.
Proposal
As part of our discussion at #29665 (closed) we have concluded that we should make two changes to the gitlab-runner register API.
When using the new process (glrt prefix):
- runner should only be verified at the end of the
gitlab-runner registercommand - logic to delete (API call
unregister) when the process is aborted is removed (means the runner is never unregistered)