Enable auto-startup for DefaultMessageListenerContainer

[jhl221123]

This PR modifies DefaultMessageListenerContainer to enable auto-startup by default, allowing it to participate more fully in the Spring container-managed lifecycle.

Key changes:

• Introduced an autoStartup boolean property (defaulting to true), making isAutoStartup() return this value.
• A public setter setAutoStartup(boolean) allows users to disable this behavior if necessary.

Closes #4403

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