SpringBoot Perform failure analysis when a web application cannot be started due to a missing web server factory bean

Hi, I submitted this PR to solve #28926.

I'm not sure if MissingWebServerFactoryBeanException should inherit ApplicationContextException and if MissingWebServerFactoryBeanException should be thrown upwards.

https://github.com/spring-projects/spring-boot/blob/4e62ac458f5682f946e4985d0aee41c8b720c47b/spring-boot-project/spring-boot/src/main/java/org/springframework/boot/web/reactive/context/ReactiveWebServerApplicationContext.java#L81-L82

Closes gh-28926

Comment From: terminux

Thank you for using your precious time to review my code @wilkinsona. I updated the PR and it's ready for your review again.

Comment From: wilkinsona

Thanks for the latest updates, @terminux. I'm going to label this one for a forthcoming meeting so that we can discuss the package of the new MissingWebServerFactoryBeanException class.

Comment From: wilkinsona

Thank you, @terminux.