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

• You have read the Spring Data contribution guidelines.
• You use the code formatters provided here and have them applied to your changes. Don’t submit any formatting related changes.
• You submit test cases (unit or integration tests) that back your changes.
• You added yourself as author in the headers of the classes you touched. Amend the date range in the Apache license header if needed. For new types, add the license header (copy from another file and set the current year only).