Return union types on query/mutation resolvers

[jeggy]

We should add support for returning union types in query and mutation resolvers. As it states in the documentation this is not supported in all scenarios(https://kgraphql.io/Reference/Type%20System/unions/)

Currently there is a limitation on union return types for query definitions. This is currently only supported via sealed classes. See more information below.

[tomperi-nr]

Hey @jeggy, any updates on this? Is it possible to return a Union based on interface and reflection? This is really important for me, and I might have some time to implement it, can you point me in the right direction?