Prohibit bean overriding by default and analyze override failures

Closes gh-13609

spring-boot-project/spring-boot-docs/src/main/asciidoc/appendix-application-properties.adoc

@@ -113,6 +113,7 @@ content into your application. Rather, pick only the properties that you need.
 	spring.mail.username= # Login user of the SMTP server.
 
 	# APPLICATION SETTINGS ({sc-spring-boot}/SpringApplication.{sc-ext}[SpringApplication])
+	spring.main.allow-bean-definition-overriding=false # Whether bean definition overriding, by registering a definition with the same name as an existing definition, is allowed.
 	spring.main.banner-mode=console # Mode used to display the banner when the application runs.
 	spring.main.sources= # Sources (class names, package names, or XML resource locations) to include in the ApplicationContext.
 	spring.main.web-application-type= # Flag to explicitly request a specific type of web application. If not set, auto-detected based on the classpath.