fix: declare opentelemetry-semantic-conventions for aio-pika, logging, pika and system-metrics (#4594)

* fix: declare opentelemetry-semantic-conventions for four instrumentations

The aio-pika, logging, pika and system-metrics instrumentations import
opentelemetry.semconv directly but only resolved it transitively through
opentelemetry-instrumentation. Declare it explicitly in each pyproject.toml
so the package metadata reflects the actual imports, following up on #4590.

* Rename changelog fragment to PR number

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Co-authored-by: Emídio Neto <9735060+emdneto@users.noreply.github.com>