Add support for YAML format

[milehimikey]

Feature request to add yaml format to the /springwolf/docs endpoint. This can be useful for certain tools that work from YAML files to render AsyncAPI documentation.

[Crain-32]

See https://stackoverflow.com/questions/58414715/generate-yaml-format-response-in-springboot for possible solution for integration. You'd just have to have a second @GetMapping that produces the normal json.

[stavshamir]

Json could be easily translated to yaml with external tools. Maybe this can be added as a feature for the UI in the future as an export button.