Integrate partial reindexing with mode_async bulk reindexing

[abdul-wahab-qbatch]

I have a use case where I need to do partial bulk reindexing, though I've created my own custom workers to do so, but I want support from search kick by default.
code

index = Product.reindex(:sales_data, mode: :async)
Product.search_index.promote index[:index_name]

but the index instead of returning the index_name, returns true.
Need this support so that we can use the Searchkick::BulkReindexJob to do this.