Draft: Spike to add pagination support for tree entries retrieval

This tests out the changes in gitaly!3611 (merged). This merge request should NOT be merged, and is only intended to flush out issues.

To use this in your GDK:

1. cd gitaly
2. git checkout sh-paginate-tree-entries
3. make
4. gdk restart gitaly
5. gem build gitaly.gemspec
6. gem install gitaly-14.1.0.pre.rc4.gem

Then check out this branch:

1. bundle install
2. gdk restart rails

Test this project with https://gitlab.com/fdroid/fdroiddata/ and the metadata directory.

Relates to #334140 (closed)