Using Duckling on the Entity Schema

[PedroLucasCM]

Proposed changes:

• I used Duckling confidence_type to resolve problems on the Entity schema just like advised on this issue: https://rasa-open-source.atlassian.net/browse/OSS-517 in the openapi file (rasa.yml)

Status (please check what you already did):

• [ ] added some tests for the functionality
• [ ] updated the documentation
• [ ] updated the changelog (please check changelog for instructions)
• [ ] reformat files using black (please check Readme for instructions)