feature: hydrate AsyncPG span attributes at creation (#3841)

* feature: hydrate AsyncPG span attributes at creation (#3643)

* opentelemetry-instrumentation-asyncpg: ensure sampler sees span attributes

* tests: fix import order in asyncpg docker tests

* tests: expect net.transport in asyncpg sampler attributes

* tests: use sdk tracer in asyncpg sampling checks

* changelog: move asyncpg fix to Unreleased

* Update CHANGELOG.md

* Update CHANGELOG.md

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