[core] Setting attributesForFaceting from the config overrides Algolia settings

# Situation

When a configuration includes `custom_settings.attributesForFaceting`, the index's setting `attributesForFaceting` does not include `tags` anymore. This override the `default_settings` defined by the strategy. `tags` defined from `start_urls` are not longer handled as `attributesForFaceting`

# Result:

It might broke the search for owner filtering over `tags` and break the search. Happens a lot with people using meta tags.

# Workaround

Make sure configuration defines `tags` as a item from the collection `custom_settings.attributesForFaceting`

Start by tracing how custom_settings.attributesForFaceting and the strategy's default_settings are combined. Verify that tags from start_urls remain included in the index's attributesForFaceting, and confirm the owner-filtering search behavior after the settings are applied.

Written by the indexing model from the issue text.