[DEPRECATED] Creates a workflow custom field selection

curl --request POST \
  --url https://api.rootly.com/v1/workflows/{workflow_id}/custom_field_selections \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/vnd.api+json' \
  --data '{
  "data": {
    "type": "workflow_custom_field_selections",
    "attributes": {
      "workflow_id": "<string>",
      "custom_field_id": 123,
      "incident_condition": "ANY",
      "values": [
        "<string>"
      ],
      "selected_option_ids": [
        123
      ]
    }
  }
}'

{
  "data": {
    "id": "2",
    "type": "workflow_custom_field_selections",
    "attributes": {
      "custom_field_id": 168,
      "workflow_id": "f40c050f-eb1d-413a-b240-b0e58b3cff83",
      "incident_condition": "ANY",
      "values": [],
      "selected_option_ids": []
    }
  }
}