Extend Bulk Service to use an External Scroller

Today, the Bulk Service handles the scrolling part. A part which is not useful when ids are already materialized in a stream.

We would like to introduce an external scroller type, that does nothing, in order to disable the scrolling part of the Bulk Service. We also need to add the APIs below:

• BulkCommand.Builder#useExternalScroller in order to enable this feature
• BulkService#appendExternalBucket in order to send bulk bucket to the right stream
• BulkService#completeExternalScroll in order to complete scrolling (mainly for BulkStatus mechanism)

Example of usage:

BulkCommand command = new BulkCommand.Builder(ACTION_NAME, null, "system").useExternalScroller().build();
String commandId = bulkService.submit(command);
...
BulkBucket bulkBucket = new BulkBucket(commandId, idsList)
bulkService.appendExternalBucket(bulkBucket);
...
bulkService.completeExternalScroll(commandId, total);