[Reporting] CSV report contents are incorrectly encoded to base64

Problem: Recently, I noticed that Reporting is encoding CSV file contents to base64. This does not occur in earlier version of Kibana, and should not be happening.

Reporting was designed to encode report contents to base64, but should be doing so only when the content type is binary, such as PDF/PNG.

+ curl -k -u redacted:redacted 'https://redacted/.kibana-reporting*/_search?filter_path=hits.hits._id,hits.hits._source.created_by,hits.hits._source.payload.title,hits.hits._source.output.content&pretty'
{
  "hits" : {
    "hits" : [
      {
        "_id" : "0954be17-9c45-47ed-b315-2b1399f5268c",
        "_source" : {
          "created_by" : "elastic",
          "payload" : {
            "title" : "Untitled discover search"
          },
          "output" : {
            "content" : "bWVzc2FnZSwibWVzc2FnZS5rZXl3b3JkIgpoZWxsbzEsaGVsbG8xCg=="
          }
        }
      }
    ]
  }
}

elastic / kibana

[Reporting] CSV report contents are incorrectly encoded to base64 #202580