群组统计接口

实现下列接口：

type Group {
  members: GroupMemberConnection
  member(userId): GroupMemberEdge
}

type GroupMemberConnection {
  nodes: [User!]
  edges: [GroupMemberEdge!]
  # ...
}

type GroupMemberEdge {
  node: User!
  cursor: String!
  # ...
  exercisePacks: GroupMemberExercisePackConnection
  exercisePack(exercisePackId): GroupMemberExercisePackEdge
}

type GroupMemberExercisePackConnection {
  nodes: [ExercisePack!]
  edges: [GroupMemberExercisePackEdge!]
  # ...
}

type GroupMemberExercisePackEdge {
  node: ExercisePack!
  cursor: String!
  lastSession: ExercisePackSession
  onsiteSession: ExercisePackSession
}