Update provider credentials

curl --request PUT \
  --url https://api.novu.co/v1/subscribers/{subscriberId}/credentials \
  --header 'Authorization: <api-key>' \
  --header 'Content-Type: application/json' \
  --data '{
  "providerId": "slack",
  "integrationIdentifier": "<string>",
  "credentials": {
    "webhookUrl": "https://example.com/webhook",
    "channel": "general",
    "deviceTokens": [
      "token1",
      "token2",
      "token3"
    ],
    "alertUid": "12345-abcde",
    "title": "Critical Alert",
    "imageUrl": "https://example.com/image.png",
    "state": "resolved",
    "externalUrl": "https://example.com/details"
  }
}'

{
  "data": {
    "_id": "<string>",
    "firstName": "<string>",
    "lastName": "<string>",
    "email": "<string>",
    "phone": "<string>",
    "avatar": "<string>",
    "locale": "<string>",
    "channels": [
      {
        "providerId": "slack",
        "integrationIdentifier": "<string>",
        "credentials": {
          "webhookUrl": "https://example.com/webhook",
          "channel": "general",
          "deviceTokens": [
            "token1",
            "token2",
            "token3"
          ],
          "alertUid": "12345-abcde",
          "title": "Critical Alert",
          "imageUrl": "https://example.com/image.png",
          "state": "resolved",
          "externalUrl": "https://example.com/details"
        },
        "_integrationId": "<string>"
      }
    ],
    "topics": [
      "<string>"
    ],
    "isOnline": true,
    "lastOnlineAt": "<string>",
    "__v": 123,
    "data": {},
    "timezone": "<string>",
    "subscriberId": "<string>",
    "_organizationId": "<string>",
    "_environmentId": "<string>",
    "deleted": true,
    "createdAt": "<string>",
    "updatedAt": "<string>"
  }
}