Creates a severity

curl --request POST \
  --url https://api.rootly.com/v1/severities \
  --header 'Authorization: Bearer REPLACE_BEARER_TOKEN' \
  --header 'content-type: application/vnd.api+json'

{
  "data": {
    "id": "c524d306-62b8-48f5-9147-298dfa50f491",
    "type": "severities",
    "attributes": {
      "name": "P0",
      "slug": "p0",
      "description": "High Priority",
      "severity": "medium",
      "color": "#E58A1F",
      "position": 1,
      "notify_emails": [
        "hello@rootly.com",
        "world@rootly.com"
      ],
      "slack_channels": [
        {
          "id": "C03MKDSEJE8",
          "name": "elastisearch"
        }
      ],
      "slack_aliases": [
        {
          "id": "S03F7QUV7F1",
          "name": "leadership"
        }
      ],
      "created_at": "2025-03-07T00:09:17.550-08:00",
      "updated_at": "2025-03-07T00:09:17.550-08:00"
    }
  }
}