Clarify behavior when both (named and provided query) are configured through `@Query`

[mp911de]

We should clarify what should happen when a query annotation is configured with a query and a named query:

@Query(value="select * from User", name = "User.findBySpringDataNamedQuery")

Right now, the provided string query is used. Ideally, we do something towards helping to understand that such a configuration creates ambiguity.

See also spring-projects/spring-data-jpa#2319.

[mp911de]

We use the declared query string and not named queries. Let's add a warn logging in that cases.