Fix problem when uploading file using form-data in jersey2 client (#12563)

* Fix problem when uploading file using form-data in jersey2 client

* Remove serialization that is not required for most cases

* Small fix

samples/openapi3/client/extensions/x-auth-id-alias/java/jersey2-java8/src/main/java/org/openapitools/client/ApiClient.java

@@ -1069,7 +1069,7 @@ public class ApiClient extends JavaTimeFormatter {
         queryParams,
         allHeaderParams,
         cookieParams,
-        serializeToString(body, formParams, contentType, isBodyNullable),
+        null,
         method,
         target.getUri());