Resolve "Rework test suite to allow dead code to be removed"
This MR introduces a Gitaly service to the CI pipeline and uses it to perform integration tests that exercise the workhorse-gitaly interface.
Workhorse also has some code that is exercised by running git
locally. This is never used in production, and since the new integration tests exercise the same code, we can now remove the "local git" mode of operation.
Closes #141 (closed)