Create name? method for booleans

What does this Merge Request do?

This MR allows boolean settings to be accessed with an ? at the end (predicate method) without needing a nested structure with an enabled: true|false bool, e.g.

gdk.yml*

gdk:
  some_setting1:
    enabled: true
  some_setting2: true

Before

config.some_setting1?  # ✅ Worked 
config.some_setting2?  # ❌ Did not work - raised NoMethodError: undefined method `fetch' for true:TrueClass

With this MR, config.some_setting2? now works 🙂

Related: gitlab#194156 (moved)

Merge Request checklist

• Tests added for new functionality. If not, please raise Issue to follow-up.
• This change is backward compatible. If not, please include steps to communicate to our users.
• [-] Documentation added/updated, if needed.
• [-] gdk doctor test added, if needed.