GH-232 Allow reference to a model from OpenApiContentProperty

[f1qwase]

Hi @dzikoysk,
I faced a need to send complex data along with files in a single request.
OpenAPI specification allows it: https://swagger.io/docs/specification/v3_0/describing-request-body/multipart-requests/

Currently javalin-openapi only allows description of primitive types properties in multipart/form content using fields type and format.
This PR introduces a from property to OpenApiPropertyContent annotation. The new from property is treated the same way as in OpenApiContent (it has higher priority than type and format and registers referenced type globally).

What do you think?

[dzikoysk]

Yeah, makes sense - thanks for the PR! :) Could you quickly check if it doesn't infinitely loop when a class with self-reference is used? Like:

data class Loop(val self: Loop)

It might be a good idea to add it to the existing example (or tests), just in case 😅

[f1qwase]

Hi, I added a test for the Loop class.

This PR changes the @OpenApiContentProperty annotation but I used the @OpenApiContent annotation for the loop test since it's more common used and both are processed in the same way.
Please, let me know if you want to test the @OpenApiContentProperty as well.

[f1qwase]

Hi @dzikoysk,
I wanted to follow up on the status of this PR. Are there any updates or additional changes you'd like to make?

We're currently using javalin-openapi in production and would like to start using this feature.

Thank you.

[dzikoysk]

Thanks for reminder, I just missed the notification. Looks good, thank you! It should be available as snapshot within a few minutes :)