Create batch generation

curl --request POST \
  --url https://app.gomangrove.com/api/v1/ledgers/{ledger_id}/batch_generations \
  --header 'Authorization: <api-key>' \
  --header 'Content-Type: application/json' \
  --data '
{
  "start_time": "2025-01-01T00:00:00.000Z",
  "end_time": "2025-03-31T23:59:59.000Z"
}
'

{
  "id": 1,
  "type": "batch_generation",
  "state": "processing",
  "progress": 0,
  "created_at": "2025-01-15T10:00:00.000Z"
}