Refactor http stack so external resource download reuses configured Http client #1778

Currently HttpResourceLoader use HTTPURLConnection SDK API to download external resources. It should use more modern java.net.HttpClient.
HTTP/OpenAPI use Jackata REST client to perform the http invocation.
This is intentional to allow users that are not interested on HTTP/API to not include that dependency and still being able to download http/s resources (for example a GPRC)
However the problem is that jakarta http client setup for that workflow/task (through AdditionalObject usage) is not used to download the openapi schema associated to that task.
The solution should be, if an HTTPClient additional object is setup for that worklfow/TASK, use it to download external resources. If not, use HttpClient default SDK configuration