Fixes choice field schema for OpenAPI response

[abhi1693]

Fixes: #12960 and #12644

For the example in the issue, here is the new definition

{
  "type": "object",
  "properties": {
    "value": {
      "enum": [
        "connected",
        "planned",
        "decommissioning"
      ],
      "type": "string",
      "description": "* `connected` - Connected\n* `planned` - Planned\n* `decommissioning` - Decommissioning"
    },
    "label": {
      "type": "string",
      "enum": [
        "Connected",
        "Planned",
        "Decommissioning"
      ]
    }
  }
}

For IPAddress, the schema looks like

{
  "type": "object",
  "properties": {
    "value": {
      "enum": [
        4,
        6
      ],
      "type": "integer",
      "description": "* `4` - IPv4\n* `6` - IPv6"
    },
    "label": {
      "type": "string",
      "enum": [
        "IPv4",
        "IPv6"
      ]
    }
  },
  "readOnly": true
}