List severities

curl --request GET \
  --url https://api.rootly.com/v1/severities \
  --header 'Authorization: Bearer <token>'

{
  "data": [
    {
      "id": "<string>",
      "type": "severities",
      "attributes": {
        "name": "<string>",
        "created_at": "<string>",
        "updated_at": "<string>",
        "slug": "<string>",
        "description": "<string>",
        "severity": "critical",
        "color": "<string>",
        "position": 123,
        "notify_emails": [
          "<string>"
        ],
        "slack_channels": [
          {
            "id": "<string>",
            "name": "<string>"
          }
        ],
        "slack_aliases": [
          {
            "id": "<string>",
            "name": "<string>"
          }
        ]
      }
    }
  ],
  "links": {
    "self": "<string>",
    "first": "<string>",
    "prev": "<string>",
    "next": "<string>",
    "last": "<string>"
  }
}