Support for problem details based on RFC 7807

[rstoyanchev]

This has been requested a number of times but so far has been deferred to Spring Boot which supports error response details. The corresponding spring-projects/spring-boot#19525 issue in Spring Boot has gathered quite a bit of feedback and comments.

For Spring Framework 6 we have an opportunity to revisit this topic and more generally, web error handling. Given a standard such as RFC 7807 for the format of error responses, the Spring Framework could provide more infrastructure that Boot can build on.

• Add types to represent RFC 7807 problem details and exceptions #28187
• Support "application/problem+json" as the response Content-Type #28189
• Enable access to an RFC 7807 ProblemDetail formatted error response from the client side #28190
• Allow dynamic properties in ProblemDetail #28665
• Update documentation for RFC 7807 support #28438
• Add WebFlux equivalent of ResponseEntityExceptionHandler #28439
• Allow for external customization and i8n of the "detail" of an RFC 7807 response #28814
• Add native support for ExceptionHandler and ProblemDetail #29297

[hantsy]

Spring HATEOAS includes another VndErrors API, it is based on https://github.com/blongden/vnd.error.