[kotlin-client] Add @JsonEnumDefaultValue annotation to enum class (#19380)

Author: ken-tunc

modules/openapi-generator/src/main/resources/kotlin-client/enum_class.mustache

@@ -7,6 +7,9 @@ import com.squareup.moshi.Json
 import com.squareup.moshi.JsonClass
 {{/moshi}}
 {{#jackson}}
+{{#enumUnknownDefaultCase}}
+import com.fasterxml.jackson.annotation.JsonEnumDefaultValue
+{{/enumUnknownDefaultCase}}
 import com.fasterxml.jackson.annotation.JsonProperty
 {{/jackson}}
 {{#kotlinx_serialization}}
@@ -46,7 +49,7 @@ import kotlinx.serialization.*
     @SerializedName(value = {{#lambda.doublequote}}{{{value}}}{{/lambda.doublequote}})
     {{/gson}}
     {{#jackson}}
-    @JsonProperty(value = {{#lambda.doublequote}}{{{value}}}{{/lambda.doublequote}})
+    @JsonProperty(value = {{#lambda.doublequote}}{{{value}}}{{/lambda.doublequote}}){{#enumUnknownDefaultCase}}{{#-last}} @JsonEnumDefaultValue{{/-last}}{{/enumUnknownDefaultCase}}
     {{/jackson}}
     {{#kotlinx_serialization}}
     @SerialName(value = {{#lambda.doublequote}}{{{value}}}{{/lambda.doublequote}})

samples/client/echo_api/kotlin-jvm-spring-3-restclient/src/main/kotlin/org/openapitools/client/models/StringEnumRef.kt

@@ -16,6 +16,7 @@
 package org.openapitools.client.models
 
 
+import com.fasterxml.jackson.annotation.JsonEnumDefaultValue
 import com.fasterxml.jackson.annotation.JsonProperty
 
 /**
@@ -35,7 +36,7 @@ enum class StringEnumRef(val value: kotlin.String) {
     @JsonProperty(value = "unclassified")
     unclassified("unclassified"),
 
-    @JsonProperty(value = "unknown_default_open_api")
+    @JsonProperty(value = "unknown_default_open_api") @JsonEnumDefaultValue
     unknown_default_open_api("unknown_default_open_api");
 
     /**

samples/client/echo_api/kotlin-jvm-spring-3-webclient/src/main/kotlin/org/openapitools/client/models/StringEnumRef.kt

@@ -16,6 +16,7 @@
 package org.openapitools.client.models
 
 
+import com.fasterxml.jackson.annotation.JsonEnumDefaultValue
 import com.fasterxml.jackson.annotation.JsonProperty
 
 /**
@@ -35,7 +36,7 @@ enum class StringEnumRef(val value: kotlin.String) {
     @JsonProperty(value = "unclassified")
     unclassified("unclassified"),
 
-    @JsonProperty(value = "unknown_default_open_api")
+    @JsonProperty(value = "unknown_default_open_api") @JsonEnumDefaultValue
     unknown_default_open_api("unknown_default_open_api");
 
     /**