Polymorphic types offer mutations under some circumstances?
Polymorphic types shouldn't offer mutations currently, since they don't work.

Extracted from #2077

---

I can't find a way to create a `Profile` when creating an `Individual`

In my system, a `Profile` is always one of a few given types. It is unexpected that a `Profile` should be created without an associated e.g. `Individual`. Preferably, I would like to remove `createProfile` from my mutations altogether and expose only e.g. `createIndividual`. However, this means `createIndividual` needs to be able to create the base `Profile`, which it seems is not possible?

Current
```gql
mutation {
  createIndividual(input: {individual: {
    # This is the only property available in `individual`.
    profileByRowId {
      # There are no properties available here for creating a profile
    }
  }}) {
    id
  }
}
```

Expected
```gql
mutation {
  createIndividual(input: {individual: {
    profile: {
      name: "Felix"
    }
  }}) {
    id
  }
}
```