[REQ] "dateLibrary" option for Kotlin

Created by: ackintosh

Is your feature request related to a problem? Please describe.

Even though KotlinSpringServer generates a java.time.OffsetDateTime property from date-time, I often need LocalDateTime instead.

https://github.com/OpenAPITools/openapi-generator/blob/9e1cce2e7b2fefa742c4992215c59998fb9fb311/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/KotlinSpringServerCodegen.java#L247

Describe the solution you'd like

How about that add dateLibrary option to KotlinSpringServer?

e.g. AbstractJavaCodegen

JavaCodegen allows dateLibrary=java8-localdatetime to generate java.time.LocalDateTime property.

https://github.com/OpenAPITools/openapi-generator/blob/9e1cce2e7b2fefa742c4992215c59998fb9fb311/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AbstractJavaCodegen.java#L496-L497

$ openapi-generator config-help -g java
        dateLibrary
            Option. Date library to use
                joda - Joda (for legacy app only)
                legacy - Legacy java.util.Date (if you really have a good reason not to use threetenbp
                java8-localdatetime - Java 8 using LocalDateTime (for legacy app only)
                java8 - Java 8 native JSR310 (preferred for jdk 1.8+) - note: this also sets "java8" to true
                threetenbp - Backport of JSR310 (preferred for jdk < 1.8)