Parallelize gdk update

Overview

In order to speed up gdk update, we want to parallelize some of its tasks.

For example, on every gdk update run, we spend a lot of time on compiling gitlab-org/gitlab-related projects, such as workhorse. This could be done in parallel with e.g. generating the GraphQL schema files or updating other related projects like gitlab-pages.

Impacted categories

The following categories relate to this issue:

• 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.