Add support for Upserts to ETSoapObject#update

[avelinsk]

According to the Marketing Cloud article below (1), it is possible to do an Upsert in a DataExtension. Please, provide this option also for the Fuel Java SDK.

A suggestion: maybe offer an update method, which accepts as an argument UpdateOptions to be used during creation of the UpdateRequest.

public static <T extends ETSoapObject> ETResponse<T> update(ETClient client,
                                                            List<T> objects, 
                                                            UpdateOptions updateOptions)
    throws ETSdkException
{
    ETResponse<T> response = new ETResponse<T>();

    if (objects == null || objects.size() == 0) {
        response.setStatus(ETResult.Status.OK);
        return response;
    }

    //
    // Get handle to the SOAP connection:
    //
    ETSoapConnection connection = client.getSoapConnection();

    //
    // Automatically refresh the token if necessary:
    //
    client.refreshToken();

    //
    // Perform the SOAP update:
    //
    Soap soap = connection.getSoap();

    UpdateRequest updateRequest = new UpdateRequest();
    updateRequest.setOptions(updateOptions);
    for (T object : objects) {
        object.setClient(client);
        updateRequest.getObjects().add(object.toInternal());
    }

The UpdateOptions can receive a SaveAction.UPDATE_ADD

SaveOption upsertOption = new SaveOption();
upsertOption.setSaveAction(SaveAction.UPDATE_ADD);
upsertOption.setPropertyName("dataExtensionName");

UpdateOptions option = new UpdateOptions();
List<SaveOption> saveOption = option.getSaveOptions().getSaveOption();
saveOption.add(upsertOption);

(1) https://help.marketingcloud.com/en/technical_library/web_service_guide/technical_articles/managing_data_in_data_extensions/