doc: add airbyte_secret field in example (#16374)

Author: alafanechere

docs/connector-development/tutorials/cdk-tutorial-python-http/define-inputs.md

@@ -24,6 +24,7 @@ connectionSpecification:
     access_key:
       type: string
       description: API access key used to retrieve data from the Exchange Rates API.
+      airbyte_secret: true
     start_date:
       type: string
       description: Start getting data from that date.