DefaultJmsListenerContainerFactoryConfigurer#setObservationRegistry should not be public

[vpavic]

While working on #44465 I noticed that DefaultJmsListenerContainerFactoryConfigurer#setObservationRegistry (introduced in 0321a8a) is public unlike other setters in this class that are package-private. There are no usages of #setObservationRegistry outside of its package so this was likely by accident.

[snicoll]

Thanks for the report. While there isn't any usage of it, it is now public in a GA version of Spring Boot so I am not sure if we could change that in a maintenance release. Flagging for team attention to see what the rest of the team think.

[wilkinsona]

We're going to deprecate setObservationRegistry in 3.3.x onwards as it should not have been public. Once the deprecation period has elapsed, we'll make it package private. In the meantime, callers elsewhere in Boot can suppress the warning.