Migration Report download fails when resulting CSV exceeds 5MB

The migration report, available on the Migrations page following a Cloud migration, cannot be downloaded once it exceeds 5MB. Since large migrations with many errors produce larger reports, the ones most likely to need this report for troubleshooting are also the ones most likely to be blocked from downloading it.

Steps to reproduce:

1. Run a DC to Cloud migration that generates a large number of migration errors.
2. Navigate to Jira Settings > Marketplace apps > Xray > Migrations.
3. Open the migration details for the affected migration.
4. Click on "Download Report".

Expected result:

The migration report CSV downloads successfully regardless of size.

Actual result:

The download fails with the following error when the report exceeds 5MB:

{
  "errors": [
    {
      "message": "Response must not exceed 5242880 bytes in size.",
      "locations": [],
      "extensions": {
        "errorSource": "GRAPHQL_GATEWAY",
        "statusCode": 509,
        "agg": {
          "severity": "NORMAL",
          "ugcPiiSafe": true
        },
        "classification": "ResponseTooLargeException"
      }
    }
  ],
  "data": {
    "invokeExtension": null
  }
}