[kafka] Instrumentation floods debug logs

[lachmatt]

Bug Report

Symptom

v1.11.0 modified the instrumentation for messaging instrumentations, specifically Confluent.Kafka client.
Previously, activity was started after receive completed, if there was a message received.
Now, activity is started when receive starts, and discarded when receive ends, when no message was received.
This frequent starting and discarding of activities, especially when Consume with CancellationToken is used (which polls every 100ms by default), results in a lot of noise in our instrumentation logs, when OTEL_LOG_LEVEL is configured with a value of debug (which is documented to be used only during troubleshooting).

Setting OTEL_LOG_LEVEL to debug results in our event listener subscribing to Verbose events from SDK event source.
Activity listener configured by SDK produces Verbose event any time activity is started or stopped.

When default sink type (i.e File) is used, size of log files is bounded.

[pjanotti]

SIG: @lachmatt will look into the instrumentation/SDK and also at the possibility of creating another log level "log everything" on auto-instrumentation side.