Span should provide Record Exception Method

[eddynaka]

Following the spec, span should provide a Record Exception method.

My suggestion: in the class TelemetrySpan we should provide two methods:

public TelemetrySpan RecordException(Exception ex)
{
    // TODO: actual implementation
}

public TelemetrySpan RecordException(string type, string message, string stacktrace)
{
    // TODO: actual implementation
}

With that, as spec says, add the exception as an Event.

References:

• Java: https://github.com/open-telemetry/opentelemetry-java/blob/ca85d8f0eb43aa05aa0aa18bdf92fa6b42abbfba/sdk/tracing/src/main/java/io/opentelemetry/sdk/trace/RecordEventsReadableSpan.java#L430

#assign me