SpringBoot Polish Javadoc for DockerImageNames.rabbit()

This PR polishes Javadoc for DockerImageNames.rabbit() a bit.

See gh-36610

Comment From: philwebb

Thanks @izeye. I wonder if we should drop the @since tags since all this stuff is pretty internal.

Comment From: wilkinsona

I've opened https://github.com/spring-projects/spring-boot/issues/37403 for the removal of @since.

Comment From: wilkinsona

Thanks very much, @izeye.