Consider auto-generating `uuid` and `timeuuid` partition/clustering key values for inserts

[mpenick]

When not provided to an insert maybe we could consider auto-generating uuid types for keys. It would provide similar functionality to uuid() and timeuuid(). The values could then be returned by the result.

[jorgebay]

I think we can leverage scalars and allow those functions as literals:

mutation {
  insertBooks(value: { id: "uuid()", title: "My book"}) {
    value { id, title }
  }
}