Introduce Prev/Next pagination to branches

What does this MR do?

Changes pagination controls from:

To:

It's the next step to improving the performance of Branches page: #211710 (closed).

Technical reason behind the UI change

Gitaly provides page-token pagination for branches instead of offset pagination. That means that we can't easily access a particular page of the branches list without fetching all branches from Gitaly and iterate them manually. However, page-token pagination allows us to retrieve next bunch of branches. We can use it in order to implement prev-next pagination which should work more performant.