Structured log / prometheus metrics for gitlab-qa results

I would like to be able to post the results of gitlab-qa to one of the prometheus push gateways so that we can create a dashboard view of QA runs.

To do this we could either push the metrics from the app, write a metric file that we can post, or simply a structured log from the run that is machine parsable and can be massaged into metrics for prometheus.

This is part of the effort to create a central release dashboard for CICD deployments - https://gitlab.com/gitlab-org/release/framework/issues/46 . We can probably start with pass/fail for pipeline runs but having metrics for individual test runs would be extremely useful for reporting.