Add a GitLabHQ-based benchmarky test for the constraint solver

At this point constraint solver can solve very shallow but averagely broad tests
(like sinatra + copybara + others) or very narrow but deep tests (rails).

This test is both deep and broad (the dependencies graph is huge) but it is also
a very unique case of a) mature packages ecosystem b) enourmous app (gitlabhq)

Further optimizations can be applied for this test.