`gdk version/help` and theirs aliases to skip config validation

What does this merge request do and why?

This MR ensures that both gdk version, gdk --version skip config validation.

It also allows gdk help (and it aliases) to skip config validation to improve user experience.

Finally, it moves command handling logic from GDK namespace to GDK::Command.

See individual commits for more context.

How to set up and validate locally

# Make config invalid
echo "gdk:\n  debug: 42" >> gdk.yml

gdk version
gdk --version
gdk help
gdk -h
gdk --help

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.