Draft: testing: Introduce testify/suite to remove testing boilerplate code

A common complaint when starting Gitaly development is the testing setup and associated boilerplate. It clutters the code and distracts with setup and teardown logic. Given Gitaly already uses testify/require and testify/assert it seemed testify/suite might be a good idea to use too.

These changes first aim is to remove boilerplate, without any changes in the logic.

The biggest downside I see now is that go -run=<TestName> doesn't work anymore.