Add filter to enqueue autosuggest styles when reindexing

[hugosolar]

** Problem ** We have a project that doesn't rely on ElasticPress built-in endpoint for autosuggestions, but we do rely on the styles on the frontend. So when we're running a re-index, the styles break the appearance of the site.

** Possible Solution ** Add a filter to allow enqueuing the autosuggest styles even if the site is being reindexed

Additional context This change was added here: https://github.com/10up/ElasticPress/pull/2163 because of a Javascript error, so I think enqueuing just the styles won't cause any issues