doc clarification for issue 971

[iparadiso]

https://github.com/awspring/spring-cloud-aws/issues/971

Clarify bean factory name overrides needed for a mix of @SqsListener acknowledgmentMode usages with existing custom MessageListenerContainerFactory defined in the app.

:loudspeaker: Type of change

• [ ] Bugfix
• [ ] New feature
• [X ] Enhancement
• [ ] Refactoring

:scroll: Description

Doc clarification for issue https://github.com/awspring/spring-cloud-aws/issues/971

:bulb: Motivation and Context

Helps clarify the reason for the following exception found when using custom MessageListenerContainerFactory and acknowledgementMode annotation in the same app.

No MessageListenerContainerFactory bean with name defaultSqsListenerContainerFactory found for endpoint names

:green_heart: How did you test it?

:pencil: Checklist

• [ ] I reviewed submitted code
• [ ] I added tests to verify changes
• [X] I updated reference documentation to reflect the change
• [ ] All tests passing
• [X] No breaking changes

:crystal_ball: Next steps