Unknown config keys are ignored

Overview

Currently, setting foo: bar in gdk.yml manually does not fail when running gdk config list.

After saving GDK config unknown keys are simply ignored.

Proposed solution

GDK should warn whenever unknown keys are detected.

Later, we could use this fact to trigger automatic config migration (#2362 (closed)).

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.

Steps to replicate (optional)

Proposal (optional)

Environment (optional)

• Operating system name: <!-- output of `uname -a` command -->
• Architecture: <!-- output of `arch` command -->
• The contents of your gdk.yml (if any)
• Ruby version: <!-- output of `ruby --version` command -->
• GDK version: <!-- output of `git rev-parse --short HEAD` command -->