Record API: Allow configurable inlining of parent record for 1:1 and 1:N relations

[ignatz]

As discussed with @svicknesh in #25, API's JSON schema could be modified to look something like:

type Comment = {
  id: string,
  user: {
    id: string,
    data: User | undefined,
  }
  tags: {
    data: Tag[] | undefined,
  }
}

the behavior would need to be configurable on the root API level to avoid accidentally leaking private records. Additionally, the behavior could be controlled on the per request level through a param like ?expand=user,tags.