Create a separate module for JMH benchmarks

Is your feature request related to a problem? Please describe. There are multiple implementations of the SpanProcessor interface. I'd like to compare their performance to pick the one that best fulfils my requirements. Currently, one has to copy benchmarking classes like BatchSpanProcessorBenchmark, BatchSpanProcessorCpuBenchmark etc. Moreover, helper classes like BatchSpanProcessorMetrics also have to be copied. This leads to code duplication. When updating one class, one has to also update its clones.

Describe the solution you'd like I'd like to have a benchmarking module containing all common code: helper classes and benchmarks.

Describe alternatives you've considered Alternatively, we could leave code as it is right now.