Cosmos updates require id field on input object as well as mutation argument

Given an ObjectType defined like so:

type Planet @model {
  id: ID
  name: String
  character: Character
  age: Int
  dimension: String
  stars: [Star]
}

The following update mutation is generated:

  updatePlanet(
     id: ID!
    _partitionKeyValue: String!
    item: UpdatePlanetInput!
  ): Planet

And it requires an UpdatePlanetInput defined here:

input UpdatePlanetInput {
  id: ID
  name: String
  character: UpdateCharacterInput
  age: Int
  dimension: String
  stars: [UpdateStarInput]
}

The id parameter is required to the updatePlanet mutation, but it also appears on the UpdatePlanetInput, but it's nullable, as the update is a partial update.

When run, this will result in an error that the update has failed because the id field wasn't provided on the object passed to container.ReplaceItem.

Manually providing the value for id on the item parameter will solve this (but can run into #296, depending on how you provide the value).

It probably makes sense that if the id is not provided on the item parameter, we inject it before calling the Cosmos SDK.

Also, should we be using UpsertItem not ReplaceItem to perform the partial update against a Cosmos document?