Support gdk config set --force

Overview

As mentioned over at gitlab!105181 (comment 1211756535), on occasion there's a need to have gdk config set write the value to the gdk.yml, even if the value is the default.

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.