favorites: include favorites in bigquery exports.

Include the favorites table in the nightly database dumps in BigQuery.
Previously we couldn't do this because we didn't have an index on
the favorite ID, which we needed to iterate across the table efficiently.

Note that this doesn't include private favorites. Note also that if a
user switches their favorites from private to public, then their
favorites will begin to appear in these dumps.

app/logical/bigquery_export_service.rb

@@ -39,7 +39,7 @@ class BigqueryExportService
     Rails.application.eager_load!
 
     models = ApplicationRecord.descendants.sort_by(&:name)
-    models -= [Favorite, IpAddress, TagRelationship, ArtistVersion, ArtistCommentaryVersion, NoteVersion, PoolVersion, PostVersion, WikiPageVersion]
+    models -= [IpAddress, TagRelationship, ArtistVersion, ArtistCommentaryVersion, NoteVersion, PoolVersion, PostVersion, WikiPageVersion]
     models
   end