Add methods to get matches count or existence

[GerkinDev]

• Add has method on adapter & model to check if at least entity matches the query. It could be polyfilled with a find method, returning true if an item is matched
• Add count method on adapter & model to get the number of entities matching the query. It could be polyfilled with a findMany method, returning the count of matched items.
• Add every method on adapter & model to check if every entities matches the query. It can be polyfilled by running a findMany with the query, and check if the number of matched entities is equal to the count of entities matched by a findMany without any criterion