[Suggestion] Add `Like` in `PersistFilter`

Currently, we need to use BackendSpecificFilter to represent LIKE operator. Since there's no sanity check for wildcard characters, there's chance that they are injected via user's input.

For example, let's say we want to SELECT books LIKE authors which start with the user's input, we can write like this:

books <- runDB $ selectList [Filter BookAuthor (Left $ concat [author, "%"]) (BackendSpecificFilter "LIKE")] [Asc BookId]

If users pass inputs something like %Haskell as author, WHERE clause would be %Haskell% and the result would become books which contain Haskell, which we didn't expect.

To solve this problem, I think we need to add value Like in PersistFilter and provide helper functions like these.

Any thoughts?

Start with the PersistFilter definition in Database.Persist.Types.Base.html and compare it with the helper functions linked from Database-Persist.html. Trace how BackendSpecificFilter produces the LIKE condition, then determine the required PersistFilter value and helper behavior so user input cannot unintentionally broaden the match; done means the supported LIKE use case is represented without BackendSpecificFilter.