Draft: Fix setting values on `hash_setting` config type

What does this merge request do and why?

Fix setting values on hash_setting config type

Previously, setting a (nested) Hash failed with:

$ gdk config set object_store.connection.foo.bar x
❌️ ERROR: wrong number of arguments (given 2, expected 0)
/home/peter/devel/gitlab/gdk/lib/gdk/config_type/base.rb:31:in
`user_defined?': wrong number of arguments (given 2, expected 0)
(ArgumentError)

How to set up and validate locally

1. gdk config set object_store.connection.foo.bar x
2. gdk config set cells.instance_count 1
3. gdk config set cells.instances.0.config.foo.bar.bax y

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.