Update gitlab-runner/config.toml location

What does this merge request do and why?

This is a documentation change. The documentation to setup dockerized runner for GDK the suggests /tmp/gitlab-runner as the host folder that is shared with the container.

mkdir /tmp/gitlab-runner
docker run --rm -it -v /tmp/gitlab-runner:/etc/gitlab-runner gitlab/gitlab-runner register --run-untagged

However /tmp/gitlab-runner does not work with Docker Desktop alternatives, such as Rancher and Colima. This MR is to call out this case and suggests to use ~/gitlab-runner instead of /tmp/gitlab-runner.

Related slack discussion https://gitlab.slack.com/archives/C2Z9A056E/p1677781940663749

How to set up and validate locally

This is a documentation change.

Impacted categories

The following categories relate to this merge request:

• gdk-reliability - e.g. When a GDK action fails to complete.
• gdk-usability - e.g. Improvements or suggestions around how the GDK functions.
• gdk-performance - e.g. When a GDK action is slow or times out.

Merge request checklist

• This change is backward compatible. If not, please include steps to communicate to our users.
• Tests added for new functionality. If not, please raise an issue to follow-up.
• Documentation added/updated, if needed.
• Announcement added, if change is notable.
• gdk doctor test added, if needed.
• Add the ~highlight label if this MR should be included in the CHANGELOG.md.