Create message datapoint by DSN

The following sample is an example request body:
{
  "datapoint": {
    "value": "",
    "metadata": {
      "key1": "",
      "key2": ""
    }
  }
}

The "value" key supports the following MIME types:
- application/json
- text/plain
- application/octet-stream

"application/json" example:
{
      "datapoint" : {
          "value" : "{\"json_out\":\"Hello json message\"}"
          "metadata": {}
      }
  }

"text/plain" example:
{
    "datapoint" : {
        "value" : "Hello string message"
        "metadata": {}
    }
}

"application/octet-stream" example:
{
"datapoint" : {
        "value" : "escaped bytes in the format \u0000"
        "metadata": {}
    }
}