Add Facet count and filtering

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It's great to have a better generic backend than the one which is included. I'd really like when this frontend would allow to use more of Meilisearch's included features:

• show facets and facet values (including counts)
• allow filtering based on facet values
• show if facet counts are exhaustive or not
• (later) use patterns to detect e.g. hierarchical facets and show them in a hierarchy