Store last verified GitLab commit SHA

What does this merge request do and why?

This MR stores the last verified commit SHA from GitLab. This later allows gdk install/update to pull the last verified SHA as an option instead of always fetching the latest code from master branch. This helps avoid team members from getting blocked by the latest changes in sub-projects like gitlab and gitaly.

I use the update verify job for verification because it handles the most of the tasks that team members perform daily. It updates the code to the latest version, sets up any dependencies, and runs database migrations.

Closes #1868 (closed)

How to set up and validate locally

Once this MR is merged, we'll be able to see the last verified commit SHA on GitLab pages.

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.