Add option to skip importing records when reindexing

I think we need options to skip importing records when reindexing a model e.g `Product.reindex`

This could be useful on development with lot records (hundreds of thousand or millions records).
Let say I have defined/modified some mapping and settings at `Product`. I have to wait all records being imported so that new mapping, settings, analyzer to take effect.

I know this is very specific use case but would be nice if we have this feature.