RESTEasy Reactive: SSE endpoints should have the same content type automatically selected as normal endpoints

[snowdrop-bot]

If we can infer the right default content-type for String and JSON for normal methods, we should do the same for this sort of SSE endpoint:

    @Path("stream")
    @GET
    @Produces(MediaType.SERVER_SENT_EVENTS)
// this should be inferred
    @RestSseElementType(MediaType.APPLICATION_JSON)
    public Multi<Fruit> sse(){
        return processor;
    }

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https://github.com/quarkusio/quarkus/issues/15778

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$upstream:15778$