fix(confluent-kafka): declare opentelemetry-semantic-conventions as a direct dependency (#4590)

* fix(confluent-kafka): declare opentelemetry-semantic-conventions as a direct dependency

The confluent-kafka instrumentation imports opentelemetry.semconv directly
in __init__.py and utils.py, but pyproject.toml only resolved it transitively
through opentelemetry-instrumentation. Declare it explicitly so the package
metadata reflects its actual imports, matching the kafka-python sibling.

* Update uv.lock for the opentelemetry-semantic-conventions dependency

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