[Kotlin] Fix (de)serialization of enum classes

While inner enum classes from dataClass.mustache work fine, standalone enum classes lack `@JsonProperty` annotations so that Jackson uses names instead of values.

Author: cschramm

modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/KotlinSpringServerCodegen.java

@@ -538,8 +538,10 @@ public Map<String, Object> postProcessModelsEnum(Map<String, Object> objs) {
                 .filter(cm -> Boolean.TRUE.equals(cm.isEnum) && cm.allowableValues != null)
                 .forEach(cm -> {
                     cm.imports.add(importMapping.get("JsonValue"));
+                    cm.imports.add(importMapping.get("JsonProperty"));
                     Map<String, String> item = new HashMap<>();
                     item.put("import", importMapping.get("JsonValue"));
+                    item.put("import", importMapping.get("JsonProperty"));
                     imports.add(item);
                 });
 

modules/openapi-generator/src/main/resources/kotlin-spring/enumClass.mustache

@@ -4,6 +4,6 @@
 */
 enum class {{classname}}(val value: {{dataType}}) {
 {{#allowableValues}}{{#enumVars}}
-    {{&name}}({{{value}}}){{^-last}},{{/-last}}{{#-last}};{{/-last}}
+    @JsonProperty({{{value}}}) {{&name}}({{{value}}}){{^-last}},{{/-last}}{{#-last}};{{/-last}}
 {{/enumVars}}{{/allowableValues}}
 }