List sources

curl --request GET \
  --url https://api.portable.io/v2/sources \
  --header 'Authorization: Bearer <token>'

{
  "data": {
    "0": {
      "id": 80190,
      "displayName": "John Doe's Google Calendar",
      "sourceSpec": "google_calendar",
      "createdAt": "2023‐06‐12T20:03:00Z",
      "updatedAt": "2023-08-01T00:00:00Z"
    },
    "1": {
      "id": 80562,
      "sourceSpec": "freshsales",
      "createdAt": "2023‐06‐12T20:03:00Z",
      "updatedAt": "2023-08-01T00:00:00Z"
    }
  }
}