sdk/log: Add processor benchmarks

[pellared]

Towards #5219

Towards #5054

This benchmarks are supposed

• Validate the the Processor interface design from performance perspective. E.g. they are used to check if a processor that is modifying a log record is causing an additional heap allocations.
• Benchmark the processors supported by the SDK.

These are "almost-end-to-end" benchmarks (with noopExporter) so that it checks the performance of the SDK log processing without the actual exporting part.

I find such kind of benchmarks very important as an addition to more fine-grained benchmarks. For me these kinds of benchmarks are like "integration tests" and more fine-grained benchmarks are like unit tests.

cpu: Intel(R) Core(TM) i9-10885H CPU @ 2.40GHz
BenchmarkProcessor/Simple-16         	 1990946	       644.6 ns/op	     417 B/op	       1 allocs/op
BenchmarkProcessor/Batch-16          	  835135	      1211 ns/op	     597 B/op	       0 allocs/op
BenchmarkProcessor/ModifyTimestampSimple-16         	 1782510	       644.3 ns/op	     417 B/op	       1 allocs/op
BenchmarkProcessor/ModifyTimestampBatch-16          	  945699	      1222 ns/op	     637 B/op	       0 allocs/op
BenchmarkProcessor/ModifyAttributesSimple-16        	 1570214	       717.6 ns/op	     465 B/op	       2 allocs/op
BenchmarkProcessor/ModifyAttributesBatch-16         	  768399	      1383 ns/op	     653 B/op	       1 allocs/op