Grant PERFMON capability to `ghc-perf-runner`
This capability allows the GitLab jobs that run on this runner to
gather performance statistics obtained using the perf system tool.
We expect certain perf PMU events to give a more accurate picture of
the run-time performance of a test than number of allocated bytes.
We modify the gitlab-runner register call, to grant jobs that run on
this runner the PERFMON capability. This may have some security
implications, as it allows malicious actors to query the underlying
system for certain PMU events.
Unfortunately, we can't be as fine-grained to only allow certain PMU events
that we actually need in CI.
References: