Proposal: Add expected attendee count to Activity list

[nathansalter]

Something that may help the taxonomy when searching or building systems is adding an 'expected attendee count' parameter to the activities. This would enable brokers which are unfamiliar with all of the sporting activities to provide simple validation prompts or suggested values when Customers are filling out 'number of attendees' forms for example.

e.g.

  {
    "@type": "Concept",
    "@id": "https://openactive.io/activity-list#ab4a33f2-dc13-4f7f-afa4-a3184dc00eab",
    "prefLabel": "Baseball",
    "inScheme": "https://openactive.io/activity-list",
    "expectedAttendeeCount": {
      "min": 10,
      "max": 18
    }
  }