Spring Issue #26985 change date time default formate

Link of issue: https://github.com/spring-projects/spring-framework/issues/26985

Issue: DateTimeFormatterRegistrar should use ISO formats by default

Currently, if the users want to format the time in ISO format, they need to annotate the controller method by @DateTimeFormat(iso = ISO.DATE_TIME). However, the issue is using ISO format should be a default setting without any configuration. For this issue, I looked into the DefaultFormattingConversionService class and there is an addDefaultFormatters method, which specifies the default handling of date-time values. To make the ISO format the default setting, I first create a DateTimeFormatterRegistrar instance and then invoke setUseIsoFormat(true). Finally, register this formatter through the FormatterRegistry which is passed in as the argument.

Comment From: sbrannen

Thanks for the PR, @Yin-Jui.

Unfortunately, the PR drops support for standard date/time formats as well as Joda Time. In addition, we will need to update tests and documentation in the reference manual. We may need to perform some other actions as well.

That's why issue #26985 is labeled status: pending-design-work (for design work to be performed by the core team) and currently slated for 6.0 M1. Thus the team will look into this topic later this year.

In light of that I am closing this PR.