Add a section about upgrading to Spring Boot 4.x #47916
Description
https://docs.spring.io/spring-boot/upgrading.html has a section for Spring Boot 2 and Spring Boot 3. We should add one for consistency targeted at Spring Boot 4.
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https://docs.spring.io/spring-boot/upgrading.html has a section for Spring Boot 2 and Spring Boot 3. We should add one for consistency targeted at Spring Boot 4.