Update GDK's .tool-version file to be just its dependencies only

Overview

Currently, the GDK has a checked in .tool-versions file that contains all required third-party software to install. It has worked well, but there are some shortcomings:

• When an upstream project updates its .tool-versions file, we need to carefully align a GDK MR with the change to ensure compatibility
• It's not possible to mark certain software as 'optional', e.g. minio or 'testing' versions of Ruby, PostgreSQL, etc.

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.

Proposal

Currently the GDK's .tool-versions file is updated by running support/asdf-combine which takes into account the checked in .tool-versions-gdk file as well as lots of upstream project's .tool-versions files.

Let's make the .tool-versions file only contain GDK's dependencies only and update all other logic to ensure when executing, the working directory is changed into the specific project (e.g. gitlab/) so asdf can gather its requirements and launch from there.