OpenTelemetry tracing errors should use RecordError function

[lucasoares]

OpenTelemetry contains two functions called RecordError and SetStatus on the span struct to record errors in the spans.

Currently, this is how we are storing errors on spans:

		span.SetTag("error", "true")
		span.LogKV(
			"event", "error",
			"type", err.Error(),
		)

This doesn't follow OpenTelemetry's specification on error handling, and then spans will not be tagged as an "error" on tracing visualization platforms.

Since we have this on the docs:

WARNING: Although the configuration spec of this component is stable the format of spans, tags and logs created by Benthos is subject to change as it is tuned for improvement.

We can change the behavior, right?