update BatchDataSender to show the cause of IOException

[vinicius-roc]

BatchDataSender was updated to show the cause of IOException.

In my scenario, when I try to send a metrics to new relic i received the below message.

WARN transport.BatchDataSender: IOException (message: Error posting metrics to New Relic) while trying to send data to New Relic. MetricBatch retry recommended

When i look for root cause of IOException, i found MicrometerHttpPoster that encapsule the original cause inside IOException

try {
  ...
} catch (Throwable th) {
  throw new IOException("Error posting metrics to New Relic", th);
}

So, to be able to see the root cause, I added to message

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