 Consider renaming `system.network.dropped` to `system.network.packet.dropped` 

See https://github.com/open-telemetry/semantic-conventions/pull/1694#discussion_r1889484257
It's not clear from the metric name what was dropped, would be great to clarify. 

If it turns out that we'd like to keep `system.network.dropped` or rename it to something else, this issue should track updating naming guidelines. 