Patterns should create GraphQL Interfaces instead of Unions

[Swahvay]

Patterns create unions in graphQL which is technically valid and correct, but not really useful the way patterns are implemented in Ent. They should be interfaces, and then the ents that use those patterns would implement the interfaces. This would allow the more common use case of typing a graphQL query to a pattern. E.g.,

node(id: '...') {
  ... on ProfilePattern {
    profilePicture
  }
}

Instead of having to do

node(id: '...') {
  ... on User {
    profilePicture
  }
  ... on Business {
    profilePicture
  }
}