Support OneOf on Input Objects

[Tehnix]

It seems oneOf has largely been accepted, and many GraphQL libraries have either started implementation or already rolled it out graphql/graphql-spec#825.

Is there any interest in Sangria supporting this, and would there be any technical blockers for it?

At $work we have had several cases where support for this would have made the resulting API better and more intuitive.

For inspiration, there's ongoing work in caliban here ghostdogpr/caliban#1846.

[yanns]

Yes, this can be interesting.
I don't think I'll have time to work on it in the next weeks though.