Create Bulk Artists

curl --request POST \
  --url https://server26-dot-royalti-project.uc.r.appspot.com/artist/bulk \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '{
  "artists": [
    {
      "artistName": "<string>",
      "signDate": "2023-12-25",
      "label": "<string>",
      "externalId": "<string>",
      "users": [
        "<string>"
      ],
      "split": [
        {
          "user": "<string>",
          "share": 123
        }
      ]
    }
  ]
}'

{
  "message": "Bulk artist creation completed",
  "createdArtists": [
    "Artist One",
    "Artist Two"
  ],
  "processedCount": 3,
  "errors": [
    "Artist Three already exists"
  ]
}