Update markdown example to yml

[yennycheung]

Proposed changes:

• See Docs for GET /conversations/<conversation_id>/story endpoint shows markdown example instead of yaml #6762
• Modify markdown example of GET /conversations/<conversation_id>/story to yml

Note for reviewer:

• I looked into https://github.com/RasaHQ/rasa/blob/master/rasa/cli/initial_project/tests/test_stories.yml and guessed the format for how the story should look like. 😅 I could be completely off.

To do:

• There are other examples with markdown, after I get the first feedback I'll update those too.
• Looks like there are some css issues as well, the example has a white background, I might fix it while I'm at it.
  

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)

[CLAassistant]

All committers have signed the CLA.

[m-vdb]

Nice, thanks for taking these changes over 💯

I left a couple of comments. Additionally, could you update other text/markdown content in this rasa.yml file? I think that the spec for /model/test/intents and /model/test/stories can be updated, as they now accept yml request bodies (and this is the default now).

[m-vdb]

Looks like there are some css issues as well, the example has a white background, I might fix it while I'm at it.

@yennycheung about that, it might be a bit more complicated than that. Since things are still a bit WIP on the API spec, I think it's better to put that on @lunelson 's radar so that he knows about it (he is in charge about our docs theme, among other things)

[yennycheung]

Looks like there are some css issues as well, the example has a white background, I might fix it while I'm at it.

@yennycheung about that, it might be a bit more complicated than that. Since things are still a bit WIP on the API spec, I think it's better to put that on @lunelson 's radar so that he knows about it (he is in charge about our docs theme, among other things)

Yeah I agree with you, I was just taking a look at the theme. I'll focus on the markdown changes then. :)

[m-vdb]

almost there 💪 only one example to change

[m-vdb]

🐩

[lunelson]

@yennycheung @m-vdb this CSS conflict is on my radar, it will be fixed this week.