Spec compliance matrix: C++ Declarative Configuration

[marcalff]

Fixes #

Changes

Please provide a brief description of the changes here.

• Spec compliance matrix: C++ now supports Declarative Configuration:
  • Cpp issue

For non-trivial changes, follow the change proposal process.

• Related issues #
• Related OTEP(s) #
• Links to the prototypes (when adding or changing features)
• CHANGELOG.md file updated for non-trivial changes
• Spec compliance matrix updated if necessary

[marcalff]

cc @open-telemetry/configuration-maintainers