Allow per document index operations on BulkAll

[russcam]

The BulkAll helper introduced in master is really helpful for setting up bulk indexing. It could be even more helpful if per document modifications were allowed to each bulk index operation. For example, it's not possible to bulk index a collection of child documents with the helper and set the _parent for each index operation.

[budzynski]

I think it is related to this issue - there is no option to specify op_type (OpType) for bulk indexing.

[Mpdreamz]

@budzynski there is no op_type in the _bulk api but you can call different actions e.g index/create/update/delete.

Thanks for voicing your need here though since I've opened up #2402 which will allow you to control in a more general fashion then this ticket requested how the buffer of IList<T> is translated into a BulkRequest using the BulkAll helper 👍