Allow for async association reindex

[gbxl]

Is your feature request related to a problem? Please describe.
When reindexing a model, I want to trigger a reindex on some associations. Currently, I have some custom code that decides whether that association should be reindexed. If it is, I can only call association.reindex. I tried using association.reindex(async: true) but that doesn't work, the async option gets dropped when calling import_scope(relation, scope: scope) in lib/searchkick/index.rb -> def reindex

Describe the solution you'd like
Can we pass along the options to the import_scope? I tried locally and in my older version of the gem (4.1.1) it complains about refresh and mode but since the newer version of the gem already removes the refresh option, we'd just need to delete mode and we'd be good to go. I think this would be very beneficial for large associations, in order to leverage the BulkReindexer vs loading everything in batches synchronously 🤒

Happy to open a PR to handle that but wanted to check with you that I'm not missing some purposeful restriction first :)

[ankane]

Hey @gbxl, thanks for the suggestion. This is part of the plan for Searchkick 5 (#1288). I'm planning to make significant changes to the reindexing logic, so want to hold off until then.

[ankane]

Hey @gbxl, still need to add the documentation, but in Searchkick 5 (just released), you can do:

association.reindex(mode: :async)

(for full reindex, you'll still need to use async: true for now, but that'll be deprecated and changed to mode in a future release)

Thanks again for the suggestion.