YAML support

[TatianaParshina]

Hi,

Is there any plans to implement adapter to generate data in YAML format?
Rasa 3.x version does not support markdown format and supports only YAML.
https://rasa.com/docs/rasa/training-data-format

Support for JSON format will be removed in Rasa 4.0
https://rasa.com/docs/rasa/migration-guide/#nlu-json-format