feat: resolve all pivot attributes

[jaulz]

• Added or updated tests
• Documented user facing changes
• Updated CHANGELOG.md

Changes

This PR allows users to expose all pivot fields in connections in a new field pivot which resides next to node and cursor. This could be helpful in the following situation:

type Post {
  id: ID
  title: String
}

type User {
  id: ID
  name: String
  ratedPosts: [Post] @hasMany(type: CONNECTION, defaultCount: 25, edgeType: "UserPostEdge")
}

type UserPost {
  id: ID
  rating: Int
}

type UserPostEdge {
  cursor: String!
  node: Post!
  pivot: UserPost!
}

extend type Query {
  userById(id: ID! @eq): User @find
}

Now we can query the user and his rated posts like this:

query ListRatedPosts {
  userById(id: 3) {
    ratedPosts {
      edges {
        node {
          id
          title
        }
        pivot {
          id
          rating
        }
      }
    }
  }
}

Since the pivot field is now of type UserPost we can easily update the rating in these entities on the client (i.e. optimistic update) without fetching the whole list again.

Breaking changes

The change will break things in the unlikely situation that there is a pivot field within the pivot field.

[spawnia]

Thank you, released with https://github.com/nuwave/lighthouse/releases/tag/v6.33.0