Initialize rake at start and reapply `rake update`

What does this merge request do and why?

This reapplies !3816 (merged)

with fixes for #2140 (closed) self-contained commit at !3844 (05479eb8)

We initialize rake at the start so that we're loading GDK/Rakefile instead of GDK/gitlab/Rakefile when the current working directory is GDK/gitlab.

This should avoid each individual command reinitialize rake multiple times as well

How to set up and validate locally

Change working directory to GDK/gitlab and run gdk update, see if it can run smoothly.

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.