Aggregate attending stats

curl --request GET \
  --url https://api.rewind.rest/v1/attending/stats \
  --header 'Authorization: Bearer <token>'

{
  "total_events": 123,
  "attended_events": 123,
  "by_category": [
    {
      "category": "<string>",
      "count": 123
    }
  ],
  "by_event_type": [
    {
      "event_type": "<string>",
      "count": 123
    }
  ],
  "by_year": [
    {
      "year": "<string>",
      "count": 123
    }
  ]
}