[kotlin-client] Add support for integer enums in serialization for kotlin-client (#21248)

Author: CHervaudBetclic

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

@@ -43,20 +43,45 @@ import kotlinx.serialization.*
 {{#allowableValues}}{{#enumVars}}
     {{^multiplatform}}
     {{#moshi}}
+    {{#isString}}
     @Json(name = {{#lambda.doublequote}}{{{value}}}{{/lambda.doublequote}})
+    {{/isString}}
+    {{^isString}}
+    @Json(name = {{{value}}})
+    {{/isString}}
     {{/moshi}}
     {{#gson}}
+    {{#isString}}
     @SerializedName(value = {{#lambda.doublequote}}{{{value}}}{{/lambda.doublequote}})
+    {{/isString}}
+    {{^isString}}
+    @SerializedName(value = {{{value}}})
+    {{/isString}}
     {{/gson}}
     {{#jackson}}
+    {{#isString}}
     @JsonProperty(value = {{#lambda.doublequote}}{{{value}}}{{/lambda.doublequote}}){{#enumUnknownDefaultCase}}{{#-last}} @JsonEnumDefaultValue{{/-last}}{{/enumUnknownDefaultCase}}
+    {{/isString}}
+    {{^isString}}
+    @JsonProperty(value = {{{value}}}){{#enumUnknownDefaultCase}}{{#-last}} @JsonEnumDefaultValue{{/-last}}{{/enumUnknownDefaultCase}}
+    {{/isString}}
     {{/jackson}}
     {{#kotlinx_serialization}}
+    {{#isString}}
     @SerialName(value = {{#lambda.doublequote}}{{{value}}}{{/lambda.doublequote}})
+    {{/isString}}
+    {{^isString}}
+    @SerialName(value = {{{value}}})
+    {{/isString}}
     {{/kotlinx_serialization}}
     {{/multiplatform}}
     {{#multiplatform}}
+    {{#isString}}
     @SerialName(value = {{#lambda.doublequote}}{{{value}}}{{/lambda.doublequote}})
+    {{/isString}}
+    {{^isString}}
+    @SerialName(value = {{{value}}})
+    {{/isString}}
     {{/multiplatform}}
     {{#isArray}}
     {{#isList}}