Add server-side pagination to SearchFilesByName

In prior versions, Wiki operations use SearchFilesByName RPC to
access files in Wiki repositories. Gitaly did not support limit
and offset. Rails has to fetch all available pages and perform
pagination from its side with Karinami. This commit adds those
fields to the corresponding request after Gitaly adds such
functionality.

Changelog: performance
Signed-off-by: Quang-Minh Nguyen <qmnguyen@gitlab.com>