Issue expressing nested required properties using attendeeDetailsRequired

[nickevansuk]

Currently it is not possible to express nested required properties using attendeeDetailsRequired, for example which properties within address are required.

The current form of attendeeDetailsRequired is as follows:

  "attendeeDetailsRequired": [
    "https://schema.org/givenName",
    "https://schema.org/familyName"
  ],

This limitation should be explicitly mentioned in the spec.