Create a body serialiser for JSON AST types

[adamw]

E.g. for ujson.Obj, so that in the example in https://scala-lang.org/blog/2023/06/20/toolkit.html we could do simply .body(ujson) instead of

  .header("Content-Type", "application/json")
  .body(ujson.write(json))

Should be the same for other JSON libs

[adamw]

@szymon-rd turns out this has worked all along :) so just doing .body(ujson) should do the trick, without having to specify the content type manually or invoking .write. Provided, of coure, the the ujson+sttp import is in place: import sttp.client4.upicklejson._