Improve logs tree fetching performance

What does this MR do and why?

This MR gets rid of a tree Gitaly call on every logs tree fetch.

The tree call only provided the following information:

• Type of an entry that helped to connect an entry and a commit
• Is there more entries to fetch?

With this MR we:

• Assume that entry names are unique and there's no need to check type
• Fetch N+1 entries to find out whether there are more entries to fetch

Testing

1. Open a project page http://127.0.0.1:3000/gitlab-org/gitlab-test
2. Make sure that Last commit are displayed and the same as before this MR