Add class name into Racecar instrumentation

[ErvalhouS]

We're actively using our Racecar instrumentation on production, it captures what we need in terms of grouped spans into transactions.

There's a difficulty looking into a specific consumer's code performance on apps that have multiple consumers/producers. That is due to the fact that the instrumentation does transaction naming as follows: process_batch, process_message, deliver_message

The ideal scenario for transaction naming in that instrumentation would be to include the class that called those methods, in a similar way as what we currently have on controller's instrumentation. Something on the lines of "#{klass}#process_batch" i.e: DopeConsumer#process_batch or DopeProducer#deliver_message