nixos/gitaly: Run gitaly with procps in scope
Gitaly uses `ps` to track the RSS of `gitlab-ruby` and kills it when it
detects excessive memory leakage. See
https://gitlab.com/gitlab-org/gitaly/issues/1562.
(cherry picked from commit b90f5f03c2d72dd81ebfbc9d5031dbcf93aa11fd)
authored by