Audit experimental-span-attributes configuration before 3.0

Is your feature request related to a problem? Please describe.

Thirty module-specific experimental-span-attributes properties remain. The name implies span-only behavior even though Instrumenter attributes can also reach metric operation listeners, and the agent knowledge articles do not explain when to use this pattern versus emit-experimental-telemetry.

Describe the solution you'd like

Before 3.0, audit these properties and migrate multi-signal umbrella switches to emit-experimental-telemetry with compatibility aliases where appropriate. Update the agent knowledge articles with the naming decision and keep semantic-convention selection separate.

Describe alternatives you've considered

Only document the existing names. This avoids migration work but preserves misleading configuration names.

Additional context

#19822 highlighted the ambiguity while reusing RabbitMQ's existing experimental attribute setting.

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