Define ports in config.rb directly

What does this merge request do and why?

This MR moves the port definitions from the port manager to the lib/gdk/config.rb file.

How to set up and validate locally

Not sure about the scope to test. Perhaps:

1. Run gdk reconfigure
2. Run gdk start
3. See that your GDK works
4. Change a port in gdk.yml
5. Run gdk reconfigure again
6. Run gdk restart
7. See that your GDK still works

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.