[BUG] [Groovy] Fix client to work with services that support other formats in addition to JSON

Author: sekikn

bin/configs/groovy.yaml

@@ -1,6 +1,7 @@
 generatorName: groovy
 outputDir: samples/client/petstore/groovy
-inputSpec: modules/openapi-generator/src/test/resources/3_0/petstore.yaml
+inputSpec: modules/openapi-generator/src/test/resources/3_0/groovy/petstore.yaml
 templateDir: modules/openapi-generator/src/main/resources/Groovy
 additionalProperties:
+  enumPropertyNaming: "original"
   hideGenerationTimestamp: "true"

modules/openapi-generator/src/main/resources/Groovy/ApiUtils.mustache

@@ -43,6 +43,7 @@ class ApiUtils {
             if (bodyParams != null) {
                 request.body = bodyParams
             }
+            request.accept = ['application/json']
             request.contentType = contentType
 
             response.success { resp, json ->