Increase ReadingLists item limit to 5k
Apparently on Android having larger than 1k lists is not that unusual.
This should not have much performance effects as queries are paged and
page sizes do not change; the only place where it matters is the
COUNT(*) query that's validating the limit on insertion, and that's
covered by an index.
Bug: T186296
Change-Id: Ia3c1e631d06cc90fdbd52b121a67f68050116f88