✨ Add native property to NluData

[jankoenig]

Proposed Changes

This PR adds a native property to the nlu property (which is part of the $input object) for each NLU integration. This way, developers can see the raw API response from the NLU service for easier debugging.

Types of Changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• My code follows the code style of this project
• My change requires a change to the documentation
• I have updated the documentation accordingly
• I have added tests to cover my changes
• All new and existing tests passed