Support draft-7 if conditional in required fields

[hx-markterry]

Support concatenation of required fields as follows

"required": [
    "type",
    "code",
    "provider",
    "supplier",
    "currency",
    "price",
    "location",
    "isCached",
    "language"
  ],
  "anyOf": [
    {
      "if": {
        "properties": { "type": { "const": "hotel" } }
      },
      "then": {
        "required": ["checkIn", "checkOut", "room"]
      }
    }
  ]