HotChocolateMissingExtend

A small repo to reproduce the issue at ChilliCream/graphql-platform#5015

The following shows the SDL output (/graphql?sdl) (trimmed for readability). Notice the Customer type is lacking the extend keyword.

schema {
  query: Query
}

# the type below should be prepended with 'extend'
type Customer @key(fields: "id") {
  id: String! @external
  customField: String!
}

type Query {
  _service: _Service!
  _entities(representations: [_Any!]!): [_Entity]!
}

...