Revert "Merge branch 'avonbertoldi/27443/graceful-shutdown-shell' into 'main'"

In !4601 (merged) we changed the generated init script (and unit file) to run runner as gitlab-user instead of root. This also changed the default runner config path to /home/gitlab-gunner/.gitlab-runner. This breaks the update workflow, where the config file already exists at /etc/gitlab-runner, but the newly generated unit file specifies /home/gitlab-runner/.gitlab-runner as the config path. This was a breaking change , so we have to roll it back ☹

I think the right thing to do is to make this a new gitlab-runner install option that is explicitly opt-in, and supersedes the --user option. We'd likely want to plumb this into the deb and rpm package installation too by allowing users to specify this option at package install time, and ultimately handle the option in packaging/root/usr/share/gitlab-runner/post-install.