Document Window<T> as a query return type

[lbruun]

Window was introduced in v3.1. It is a valid query result type.
Howver, it is missing from this table:

https://github.com/spring-projects/spring-data-commons/blob/main/src/main/antora/modules/ROOT/pages/repositories/query-return-types-reference.adoc