Support specifying MVC format for LocalDateTime/LocalTime

[trygveaa]

Currently, you can specify the format to use for parsing/formatting LocalDate with spring.mvc.date-format. However, I don't see any way to specify the format for LocalDateTime or LocalTime (except programatically register the formatter).

I would also like to be able to specify that all these three Local-classes should use the ISO 8601 format, without having to specify that format myself.

[philwebb]

Closing in favor of PR #18772