Handlebars spills through into API viewer

[KitsuneRal]

Link to problem area:
https://github.com/matrix-org/matrix-spec/blob/main/data/api/client-server/content-repo.yaml#L226 and elsewhere in the same file.

Issue
API description files can be used by code generation tools, and our own API viewer consumes them. While it's still sort of readable through the handlebars, I'd rather stick to Markdown in API files.

[turt2live]

fwiw, I did this deliberately to improve readability of the rendered spec - the fallback to text isn't great, but still readable enough.

I prefer we stay away from **Note**: syntax as much as possible, as we cannot keep the style consistent (sometimes bold, sometimes italic, sometimes lower/upper case, etc)

[KitsuneRal]

Okay, I think I agree with the rationale. That makes for an interesting precedent of using a more structured markup layer over Markdown - I wonder if there was prior art here, we are likely not the first ones stumbling over it. I don't seem to find anything quickly though.

In the meantime, what we could do then is to replace handlebars with Markdown when preparing a consolidated API description for the API Viewer; and owners of other generated code can do replacements that work best for them (e.g. for Quotient I would replace handlebars with Doxygen tags in generated C++ code).