Allow linting of config.toml files to verify configuration

Description

In the past two months, I ran into two customer tickets where the root cause was a typo in config.toml file:

• 579930 - [[runner.kubernetes.volumes.pvc]] used instead of [[runners.kubernetes.volumes.pvc]]
• 564137 - buids_dir instead of builds_dir

It would be great to have a simple command that customers could run to verify their config.toml files for such errors.

Proposal

Links to related issues and merge requests / references