[Java][Spring] Ensure EnumConverterConfiguration.java is generated when interfaceOnly=true in Spring Generator (#21000)

* Ensure EnumConverterConfiguration.java is generated when interfaceOnly=true in Spring Generator

* Add samples

Author: jorgerod

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

@@ -685,7 +685,7 @@ public void addOperationToGroup(String tag, String resourcePath, Operation opera
     public void preprocessOpenAPI(OpenAPI openAPI) {
         super.preprocessOpenAPI(openAPI);
 
-        if (!interfaceOnly && SPRING_BOOT.equals(library) && containsEnums()) {
+        if (SPRING_BOOT.equals(library) && containsEnums()) {
             supportingFiles.add(new SupportingFile("converter.mustache",
                     (sourceFolder + File.separator + configPackage).replace(".", java.io.File.separator), "EnumConverterConfiguration.java"));
         }

samples/server/petstore/spring-boot-defaultInterface-unhandledException/.openapi-generator/FILES

@@ -7,6 +7,7 @@ src/main/java/org/openapitools/api/FakeClassnameTestApi.java
 src/main/java/org/openapitools/api/PetApi.java
 src/main/java/org/openapitools/api/StoreApi.java
 src/main/java/org/openapitools/api/UserApi.java
+src/main/java/org/openapitools/configuration/EnumConverterConfiguration.java
 src/main/java/org/openapitools/model/AdditionalPropertiesAnyType.java
 src/main/java/org/openapitools/model/AdditionalPropertiesArray.java
 src/main/java/org/openapitools/model/AdditionalPropertiesBoolean.java

samples/server/petstore/spring-boot-defaultInterface-unhandledException/src/main/java/org/openapitools/configuration/EnumConverterConfiguration.java

@@ -0,0 +1,32 @@
+package org.openapitools.configuration;
+
+import org.openapitools.model.EnumClass;
+import org.openapitools.model.OuterEnum;
+
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.core.convert.converter.Converter;
+
+@Configuration
+public class EnumConverterConfiguration {
+
+    @Bean(name = "org.openapitools.configuration.EnumConverterConfiguration.enumClassConverter")
+    Converter<String, EnumClass> enumClassConverter() {
+        return new Converter<String, EnumClass>() {
+            @Override
+            public EnumClass convert(String source) {
+                return EnumClass.fromValue(source);
+            }
+        };
+    }
+    @Bean(name = "org.openapitools.configuration.EnumConverterConfiguration.outerEnumConverter")
+    Converter<String, OuterEnum> outerEnumConverter() {
+        return new Converter<String, OuterEnum>() {
+            @Override
+            public OuterEnum convert(String source) {
+                return OuterEnum.fromValue(source);
+            }
+        };
+    }
+
+}