Fix Branch API pagination with search param [RUN ALL RSPEC] [RUN AS-IF-FOSS]

What does this MR do?

When search or names params were passed, we didn't apply Gitaly pagination. But we didn't apply Kaminari pagination in this case as well.

Let's fix it by skipping Gitaly pagination when search or names params are passed.

A different feature flag is introduced: branch_api_first_page_performance