opentelemetry-instrumentation-confluent-kafka: Replace SpanAttributes with semconv constants (#4057)

* refactor: Replace SpanAttributes with semconv constants

* update CHANGELOG.md

* fix CHANGELOG.md

* Update utils.py

* Update __init__.py

* Update utils.py

* Update __init__.py

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Co-authored-by: Riccardo Magliocchetti <riccardo.magliocchetti@gmail.com>